"Let me have the fried chicken, and a steak, and the chicken fried steak."
Broken Aesop: The film starts off with Jables being ranted at by his fundamentalist Christian dad, who claims that rock and roll is evil and the work of Satan, to which JB says it's "not the Devil's work, it's magical and rad". The rest of the movie is spent searching for a pick that makes you an awesome rock star through the power of the Devil.
Broken Pedestal: Happens to Jables when he finds out that Kage isn't really a rock god, and has been living off his parents for 13 years.
Call Back: The D's part in "Beelzeboss" is strongly implied to be the song they refer to in "Tribute", as it gets referred to afterwards as "The Greatest Song In The World".
The Cameo: Neil Hamburger has a very short one as himself, performing at the same open mic night as Tenacious D themselves.
Cluster F-Bomb: Throughout the movie, but especially whenever Jables is improvising song lyrics. Just listen to "Classico".
Satan's initial boast and reaction definitely qualifies. See Oh, Crap below.
Also in "Kickapoo":
Oh the dragons balls were blazin' as I stepped into his cave, then I sliced his fuckin' cockles, with a long and shiny blade!/'Twas I who fucked the dragon, fuckaly sing-fuckaloo!/And if you try to fuck with me, then I shall fuck you too!
Foreshadowing: Jables' father warned him that the rock music would make him Satan's puppet and bring chaos to the world. He would have been right if Jables and Kage hadn't defeated Satan in the rock-off.
Fun with Acronyms: "That's where the POD lies now." "POD?" "The Pick of Destiny!" "Oh."
Heroic Fantasy: The second half of the movie, when Jables and Kage go after the Pick of Destiny, the plot basically shifts to this. I mean, it's still set in the real world, but all the tropes are there.
Kage refers to Jables as his "partner" in an awkward way in the sequence where they're apart.
Honour Before Reason: Turns out that even the Devil must abide by the Demon's Code and accept any declaration of a rock-off challenge. Keep in mind, he presumably wrote this part of the code in the first place.
Idiot Ball: JB agrees to put KG up as a bet for their rock-off with the devil...despite the Devil having said that he literally CANNOT decline a rock-off challenge.
Averted: In order to send Satan back to hell from whence he came. Jables HAD to strike a deal with him of some sort. Souls are probably the only thing The Devil would substantially benefit from (thus making it a deal), and he was about to take both their souls anyway if they lost. Plus it's quite likely that Satan, being who he is, wouldn't have let an opportunity like this slide by without specifically defining a Rock-Off as having some sort of stakes involved.
"It's a sign...a legacy." *proceeds to show birthmark on ass*
Power sliding past the security guards under the security door.
Mushroom Samba: When Jables gets lost out in the woods, he survives by eating unidentified mushrooms, which results in this trope.
Specifically, he has a trip wherein he becomes a baby sasquatch, and then begins singing about how his dad is awesome and shall protect him.
Mythology Gag: The D are met by Satan and have to play a song to save their lives (and the world). After surviving, they are unable to remember the kickass tune they played, so they try to rewrite it from scratch. Mayhaps a Tribute to that song?
No Indoor Voice: An in-story example, Jables ends up daydreaming that with the eponymous pick, his voice will become so loud he will lose any need for microphones.
Oh, Crap: The song that plays when Satan gets the pick:
Satan: I AM COMPLEEEEEEEEETE! Tenacious D: Fuuuuuuuuuuu-uuuuuuuuuuuuuuuuuuuuuck! Satan: YES, YOU ARE FUCKED! SHIT OUT OF LUCK! NOW I'M COMPLETE, AND MY COCK YOU WILL SUCK! THIS WORLD IS MINE, AND YOU'RE FIRST IN LINE! YOU BROUGHT ME THE PICK, AND NOW YOU BOTH WILL DIE! Jables: Waaaait...waaaaait! Waiiiiit, you muthafucka! We challenge you to a rock off! Give us one chance to rock your socks off! Satan: FUCK! FUCK!!(dramatically)FUUUUUUUUUUUUUUUUUUUCK... THE DEMON CODE FORBIDS ME...FROM DECLINING A ROCK-OFF CHALLENGE...
Kage gets another one during Satan's Rock Me, Asmodeus! when he reveals his collection of BDSM gear. Watch the look on his face switch from "awesome performance" to "I'm screwed" in a split second.
Satan gets yet another one when after accidentally blowing off his own horn, he realizes that he has given Jables a way to send him back to Hell.
Parental Favoritism: "You disobeyed my orders son, why were you ever born?/Your brother's ten times better than you, Jesus loves him more!"
Plot Hole: Pointed out in the DVD Commentary by Jack, during the training montage, Jables collects $10 worth of coins in a cup while performing on the boardwalk. How can he assume he collected ten exact bucks just by looking into the cup?
Soon after in the same scene, Jables goes to a nearby payphone and uses 10 cents from the cup to call Kage at home, making it $9.90. Would Jables still have enough money for the dime-bag he obtains after this scene?
Sex, Drugs and Rock & Roll: During the reunion, Kage says it was supposed to be in that order. Kage goes off to a party, Jables into the forest and eats mushrooms, and then they both get the Pick together.
Shout-Out: The Devil's guitar is Dimebag Darrell's famous lightning bolt Dean ML.
Slasher Smile: Jack Black shows his off a few times, revealing that it looks like a cross between the Joker and the Grinch.