Bad Luck Charm: A human example...for Josh, as seen in Josh Is Done where Josh stops hanging around with Drake. Without Drake around, Josh has so much more luck in life at the cost of making Drake's life far more miserable than his.
Josh: You really think we can ride the Demonator and be back before Mom and Dad get home?
Drake: Okay, let's think this through, alright? It's been 17 minutes since we were at the sign that said "Two Hours From This Point." You'd figure 1 hour and 43 minutes for the line, six minutes to ride the Demonator, 13 minutes to find the car, and 20 minutes to drive home. That puts us at the front door at exactly 10:58, so that's two minutes before Mom and Dad said they'd be home.
Josh:(beat) Okay, like if you could figure all that out, why're you failing math?
Commitment Issues: Drake goes through a different Girl of the Week every episode (sometimes he'll go through multiple girls in the same episode). He's been shown to be afraid of being steady for too long and will often get bored with his current girlfriend very quickly (possibly the only exception is Carly, the record store worker, and even she disappears eventually).
Flanderization: He just got dumber and dumber as the show progressed. At the start of the series, he was a teenager who admittedly wasn't too bright, but wasn't too dumb either. Eventually, it got to the point where he couldn't pronounce the word 'America'. As in, the country he lived in.
Mean Character, Nice Actor: Drake Bell, while not explicitly mean or a villain, is far nicer and well grounded than his character on the show.
The Millstone: "Josh Is Done" showed that Drake is really this in regards to Josh. Without having to worry about Drake's selfishness, Josh would be able to enjoy a very good life. Conversely, without Josh, Drake would fall apart. So really, Drake needs Josh more than Josh needs Drake.
No Guy Wants an Amazon: In "Girl Power," he almost dumped Lucy because he didn't want to date a girl that was stronger than he was. He only decides against dumping her when he decides that she's not at all tougher than he is, and when he tells Lucy this, Lucy challenges him to a wrestling match at his house.
Really Gets Around: Nearly every episode, he's seen with a new girl to his side, and they do always find him attractive. None of them last for long, though, even if they have a lot in common.
Screams Like a Little Girl: In "Victorious Tiberius", the neighbors called pest control after he and Josh screamed because of Mrs. Hayfer's evil dog, and they thought a pest was frightening two little girls.
Stepbrother to Drake and Megan. Josh is a very good student and a total geek, but his naive attitude in social regards and how nearly everyone doesn't like his guts (for whatever reason) drag him down many, many times.
Butt Monkey / The Chew Toy: He gets taken advantage of by Drake quite a lot and is the butt of many jokes, and on some occasions Megan or Helen will say that he has a huge head - when in actuality there's nothing wrong with his head at all. Also, his boss Helen hates him for no reason. In one episode, he's literally assaulted in the streets several times. He has been arrested several times, in fact.
If he were to stop hanging around with Drake, the universe would practically smile his way all the time.
Cool Loser: Especially towards the end of the series, when he loses weight and becomes fairly attractive. Even though he's fairly attractive, he's still treated by others (especially Drake) as a loser.
Deadpan Snarker: Especially towards Drake, but will snark at other people too.
Aww, Look! They Really Do Love Each Other: Megan is shown to genuinely care about Drake and Josh, a feeling that, for all the misery she causes him, is fully reciprocated. They were (rightly) pissed off when they found out that Megan's first boyfriend was cheating on her and resolved to get back at him for it.
Enfant Terrible: She is an evil, conniving brat (to almost preteen supervillain levels) to the titular characters, but acts sweet and adorable to everyone else.
Even Evil Has Standards: When Drake & Josh were arrested for stealing MP3 hybrids endorsed by Gary Coleman (They had merely been selling them, and had no idea the grills were stolen), they each got a phone call. When Drake made his call, he phoned home & told Megan he was in jail, who laughed it off as a prank, but when Josh phoned seconds later, there was a noticable look of concern on her face when she realized that they really were in jail, and helped the FBI arrest the real thieves.
There was also the time when Mindy framed Drake for putting their teacher's car in her classroom. Drake was likely going to lose until Megan decided to help. She even said she couldn't stand to see him sad, scared and upset like he was unless she caused it.
In "Josh Runs into Oprah," she bakes Josh a birthday cake, which Josh believes is poisoned. Megan sincerely counters that she wouldn't give him something that would make him sick on his birthday. She didn't say it wouldn't explode.
She also disapproves of eating orangutans.
Evil Genius: She even has a hidden high-tech lair in her bedroom disguised as girly toys and pictures. Seriously.
Manipulative Bitch: In one episode, to get revenge on her brothers for killing her hamster, she makes them think she's going to do something horrible to them and watches them as their fear of her revenge eats them alive.
When Josh is picked to go to work as an assistant weatherman to his dad for the day instead of Megan, Megan psyches him out by reminding him of how many people are going to be watching him in order to make him nervous so that his nervous twitch would be projected on television.
Honor Council: Helped Drake win against Mindy in the school's court.
Mindy's Back: Gives Josh a little advice when he's upset about Mindy.
Megan's First Kiss: The ending. Just see for yourself.
Drake & Josh Go to Hollywood: Megan is basically a hero in this one, as she saves her brothers from some criminals (and apparently, death because the criminals planned to kill them once they got away).
Princess Of Pranksters: Megan pulls pranks on her brothers every other week and Flanderization has turned them from harmless whoopee cushion style antics to freakily sociopathic pranks (she puts explosives in their room in one episode).
Heel-Face Turn: She wasn't outright evil towards Josh except for when she tried blaming Drake for driving Mrs. Haifer's car in the classroom and let her competitiveness take the better of her. Much later on, the two start dating and become a couple, which is ironic considering Drake never gets a single girl to stay with him.
Acquired Situational Narcissism: Happens in "Eric Punches Drake," when a rumor that Eric punched Drake for insulting Eric's sister spreads around the school. Craig gets so upset by Eric's desertion of him that he helps Drake bring Eric back down the popularity ladder by squashing the rumor.