One of the more infamous examples occurs in a filler episode of the Red Ribbon Army Saga. In this episode, a "Dr. Flappe" is credited as the creator of Android 8. Years later during Dragon Ball Z, Dr. Gero is revealed as the true creator of the androids. A later guide book would Handwave this by saying Dr. Flappe and Gero were partners on the android project.
There's a much earlier, and often ignored example of when Goku used used Nyoibou to extend and put Boss Rabbit and his Mooks on the Moon. You can likely excuse Goku for him holding his breath, but the rabbits?
The manga was in a much more comedic setting at the time, and Toriyama once stated he just didn't care. That only made thing worse when you think about the rabbits when Master Roshi (as Jackie Chun) later blew up the moon.
Big Good: Master Roshi >Kami > King Kai > Supreme Kai.
Bilingual Bonus: Shen Long is Chinese for "Dragon God." The names of almost all his alien characters - along with Bulma's family and Piccolo and his minions - are straight English or derived from it. And apparently according to Toriyama, Vegeta and Trunks use English for their attack names because he thought it sounded "more alien."
Boobs of Steel: Played straight with Ranfan, a finalist of the 21st World Martial Arts Tournament. Her entire fighting style revolves solely around flashing her boobs as a distraction (which being a Shonen manga it always works) given how she had battled her way through the Elimination round without anyone discovering her secret weapons she must logically be a very skilled martial artist when fighting fair.
Boring, but Practical: Solar Flare/Taiyoken. This attack blinds the opponent temporarily by having the user emit a light as bright as the sun. It has only failed ONCE, and that was against Omega Shenron, it works on everyone else, guaranteed. It only gets used every once once and a while for some unknown reason when the strategy of "Blind enemy then kill them while they're trying to recover" is a legitimate strategy.
Breaking the Fourth Wall: In the 8th chapter of the manga Son Goku sends Yamucha in the air with his punch but Yamucha bounces off the frame's border back to the ground.
In later chapters there are a few instances, where different characters refers to the fact that it's a manga, such as discussions of acceptableness of dirty jokes in a manga for children.
Brick Joke: Early on (in volume two of Dragon Ball), Oolong comments that Goku's amazing qualities have to be due to him being an alien. Fast forward a decade or so...
This was a complete coincidence and not a true brick joke, though. At this point the series was still at gag martial artist manga status, and given the fact that he's known for his forgetful nature, there's no way this was something Toriyama had planned all along.
However, Major Metallitron scans Goku, and it says in a corner he's not human, though doesn't know what he is. Which happened in the Red ribbon arc.
Very early on in the series, Goku, Bulma, and Oolong run into the Boss Rabbit Gang. After Goku beats up two of the grunts, they call in their boss who threatens to turn them all into Carrots. Later in DBZ, we learn Goku's Saiyan name is based off the word "Carrot." Maybe Toriyama is an Unreliable sourceof information?
Brother Chuck: Almost all of the original characters from Dragon Ball vanish completely by the end of the Buu saga. Akira Toriyama has admitted that for some of the characters it was simply because he forgot they existed, like Lunch.
Bunny-Ears Lawyer: Bulma. Taken more literally in Playboy Bunny outfit when she and Goku encountered Monster Rabbit. Her father, Dr. Briefs, also qualifies.
Muten/Master Roshi definitely counts. Imagine an elderly pervert being titled "The Invincible Master" of martial arts.
Butt Monkey: Krillin and Yamcha. This is lampshaded in Dragon Ball Z Abridged where there is an actual tally of how many times Krillin is treated like a butt monkey (the "Krillin Owned Count").
Also lampshaded in the World's Strongest movie/special. After Piccolo and Gohan are repelled by the Big Bad, Krillin flies in to take a shot, only to be knocked away before landing so much as a single punch, at which point we hear him thinking "Nope, didn't think so..."
Some of the villains such as Ninja Murasaki qualify.
Call Back: Much of the 23rd World Martial Arts Tournament contains flashbacks and comparisons to earlier in the series to juxtapose Goku as a Child and Goku as a Teenager going on Adult. This ranges from Goku's first meeting with Chi-Chi after asking her to marry him, to more subtle things like Jackie Chun/Goku knocking Yamcha/Chi-Chi out of the ring without touching them.
When Chi-Chi meets Master Roshi she doesn't believe he could be the same man who trained her father so she throws her boomerang at him, which he [[Epic Fail completely fails to block). When Goku meets Old Kai he doesn't believe he could be as strong as he says so decides to throw a energy beam at him. The dialogues
Calling Your Attacks: Blink and you miss it: Called out very early on by a Wolf who fought Yamcha in the 21st World Martial Arts Tournament. This was at a time where the only named techniques were the Kamehameha, Yamcha's Wolf-Fang Fist, and The Janken Technique.
Cheated Angle: Besides Goku's hair, the Dragon Balls themselves always have the stars in the same configuration and always facing the camera.
Chivalrous Pervert: At times, Oolong. In the 21st World Martial Arts Tournament, Bulma is standing on Oolong's shoulders to observe the elimination round while wearing a rather short skirt. One of the fighters scares Bulma and she loses here balance pulling Puar down and falling to the ground. Puar is scared and has latched on to Bulma's face, and Bulma is now scared and is flailing about. Cue Oolong staring at Bulma's panties. And then a larger group of random men. Oolong alternates between trying to block their view and getting a peek himself.
Clark Kenting: Master Roshi's "Jackie Chun" disguise involves removing his sunglasses and putting on a bad wig, and that's it. Several characters do manage to either figure it out or come close to figuring it out, but he always manages to somehow convince them that he's not Roshi after all.
With Goku you could accurately predict where they are in the battle by measuring how much its been damaged. Or even the saga itself.
Actually true for everyone to various degrees.
Collectible Card Game: Three of them, with honorable mention of DBZ being the theme of a set of Ani-Mayhem. The first game was surprisingly popular and well-liked, lasting for several years and covering all of Z and GT.
And spawning a video game as well.
The first Score of the games (they made two) still has fans who buy, sell, trade, and play the game AND it inspired the community to create an online CCG based around fixing the rules and broken play styles.
There is also a card-based battle game on the Gameboy Color called DBZ: Legendary Super Warriors. There are 125 cards in this turn-based game, some cards can be only used by specific characters. There is also a super-rare card with 'AKIRA' written on it in Japanese. To get this card you must win all of the story mode battles without losing a single match (resetting the gameboy does not count, as long as progress is not saved as a loss).
Combat Commentator: There is a recurring character who fills this role whenever a World Martial Arts Tournament is taking place. It seems like he has been announcing every single World Martial Arts Tournament since his introduction in the story during the 21st World Martial Arts Tournament. It's interesting to note the gradual change in his physical appearance as the plot progresses, with him being first introduced as a blonde, clean-shaven young man wearing a suit and sunglasses, and on the next tournament he grows a mustache, and on his most recent appearance, on the Buu Saga, he has a lankier physique and a more proiminent widow's peak on top of his mustache. This characters is also perhaps the only human other than Goku's friends who knows that it was the Z warriors, and not Mr. Satan, who have saved the Earth from all the dangers that threatened it.
Dangerous Forbidden Technique: The Mafuba/Evil Containment Wave. The original and classic Dangerous Forbidden Technique, seen specifically in the original series. Using it would allow you to seal someone (usually an baddie or Big Bad) inside of a small household object like a little jar or a electronic rice-cooker. However it always kills the user (with the sole exception of when Kami does it and Piccolo reverses it on him, and it's likely only because both weren't human that they didn't die from it), even if it fails, like Muten Roshi does when trying to stop Piccolo Daimaou.
Another possible candidate for this in a different fashion is also the dub-named "Devilmite Beam", which allows the character Akkuman to use a single move to kill anything with a speck of evil in their hearts as long as they can't regenerate themselves (luckily Goku is pure-hearted, so it fails to work on him). It doesn't have any ill effects, but it's probably considered forbidden in a different way.
Tenshinhan's Kikou-hou or Spirit Cannon is also very definitely this: a Cast From HP technique that reduces the user's lifespan every time it's used. It's powerful enough that Tenshinhan was able to temporarily stop second-tier-Cell from attacking when no one else could even touch him, to allow for the Saiyans to finish their training in the Room of Spirit and Time. This, of course, caused Tenshinhan to very nearly die (he was saved by a Senzubean, as usual).
King Kai teaches Goku two: the Genki Dama/Spirit Bomb, which is made from the life energy of everything nearby and while strong requires a huge charge up and can raze continents, and the Kaioken which briefly multiplies the users strength but leaves them drained and can seriously injure them and Goku is told to never go past 3 times his power (though Serial Escalation means that by the time he's fighting Frieza he's using it nonstop at 20 times his power to no avail)
Subverted with the Buu saga, which while still darker, has a lot more comedy than the previous arcs combined
Dark Lord on Life Support: Taopaipai and Freezer from Dragon Ball Z were both rebuilt as half-cyborg, after Goku severely damaged them, in order to survive (both had several parts of their bodies replaced by mechanical components because of the damage sustained).
David Versus Goliath: Discussed in the Ocean dub version of one Dragon Ball Z episode ("Time's Up!"), when Piccolo tells Gohan, "Remember the story of David and Goliath..." before they sense a premonition that Goku is approaching.
Dead Alternate Counterpart: Both versions of Goku contract a heart virus. Unfortunately for Future Goku, he dies from the virus. Later, most Z fighters from the alternate timeline are killed, except Future Gohan, by Android 17 and 18. Future Gohan gets killed thirteen years later.
Death Is Cheap: Every single character, with the exception of Supreme Kai and Mr. Satan, dies at least once, and only two good characters have stayed dead permanently ( the Namekian Grand Elder and Android 16).
In short, this is the poster-series for this trope. There's a reason why the fandom doesn't so much as blink when somebody good dies-they'll be revived soon enough.
Averted in the case of Piccolo before his merging with Kami; if Piccolo dies so does Kami which means the dragon balls are also gone, then all deaths are final. After Piccolo and Kami fuse back into the same being Dende becomes the new guardian of Earth, meaning that if he dies then the same thing happens.
Also averted in Future Trunks' timeline, where Piccolo and Kami are dead and Dende is still on New Namek, therefore there are no more dragon balls.
Demoted to Extra: One of the reasons why some fans prefer the original series over DBZ is that while DBZ is an infamous offender of this trope, the original series for the most part averted this.
Basically, if you appeared in the original series at all and your name wasn't Goku, Piccolo or Krillin this happened to you. Hell, even Piccolo and Krillin were sort of getting there towards the end.
The abridged series has a scene that beautifully points this out.
Denied Food as Punishment: Roshi proclaims that either Krillin or Goku will get dinner, whoever finds the rock that was thrown, and not both.
Detonation Moon: Master Roshi, as Jackie Chun, blows up the moon during the 21st Budokai Tenkaichi to stop a rampaging Oozaru Goku. Later in the series, Kami restores it, but only after he permanently removes Goku's tail...
Did You Just Punch Out Cthulhu?: Demon King Piccolo does the unthinkable after getting his big wish and blows the Dragon into pieces with one shot. At that time in the series, that was pretty much equivalent to killing God.
Arguably this happens constantly from that point onward, as every villain after that is way stronger than Piccolo.
Broke Your Arm Punching Out Cthulhu: frequently. Aside from the Mafuba (which kills the user and was used to seal Piccolo) the heroes usual end up broken with a pile of dead comrades at the end of their battles. Bonus points to Goku who by the end of his battle with Vegeta has broken every bone in his body
Disney Death: Probably an even more overused use of this trope than the trope namer itself.
Old Kai is sort of an aversion/subversion of this trope. While he does die when giving his life force to Goku, all that happens is he gets a halo because he's already in the place people go to when they die.
Dispense With The Pleasantries: When a squadron from the Red Ribbon Army comes to recruit Master Roshi, thinking he is a scientist, the leader of the group utters this phrase word for word after an extended conversation where Roshi is mocking the organization.
Doing in the Wizard : DBZ kinda does this. It doesn't do away with fantasy elements completely, mind you, but it does explain Goku and Piccolo's powers as being alien rather than supernatural. It doesn't explain all the other weird stuff in the series though...
The Dragon: Pretty much one per story arc, from Mr. Black to Commander Red all the way to Dabra to Babidi. The best example being Captain Ginyu, leader of the Quirky Miniboss Squad, The Ginyu Force, to Frieza.
Played straight by The Ocean Group dub, during his first battle against Goku, Vegeta remarks that Bardock was an average fighter, but a brilliant scientist, and yet after this there's no mention of Bardock's influence or just what he did for the Sayans in the their scientific field; of course this remark about Bardock doesn't exist in the original manga nor the japanese dub of the anime.