Class Clown

The Class Clown is...yes, Bobby?

"Please, Miss Alice. Are they a really expensive circus performers?"

Yes, very funny Mr. Showoffitz. Now, can anyone tell me why this trope is so popular? I presume you have something to add this time Bobby?

"Is it because it alliterates, miss?"

That's it Robert Showoffitz! See me after class!

This is about that one kid in the class who has to be the center of attention.

They're often a Keet or Genki Girl. Depending on how they're played they might be genuinely entertaining and popular, an Attention Whore or Bratty Half-Pint who everyone looks down upon or an annoying Jerk Jock. For added Irony they might well become a teacher after a Time Skip. Sometimes you have pairs of class clowns who are Those Two Guys, school aged Fat and Skinny are most prone to this.

They're frequently The Nicknamer and Plucky Comic Relief. In more serious works they're almost certainly a Sad Clown or Stepford Smiler. Sometimes they can be a little rough with their humour, skirting the line with The Bully at times.

Examples of Class Clown include:

Anime and Manga

The titular character of Naruto and his brother figure Iruka were both class clowns. Both acted this way out of a desperate need to not be alone any longer.
Akira Sengoku of Cage of Eden. Which is why pretty much everyone is shocked when they find out he's the one leading the most successful group of survivors.

Comic Books

The Marvel Comics' character Slapstick was a Class Clown who became a living Toon.
Mary Jane Watson-Parker (just Watson now) was one in high school, according to several Character bios, who used it to cover up her insecurities and emotional problems.
Iceman was the original Class Clown of the X-Men, but when he left, Nightcrawler took over that role.

Film: Live Action

Jeff Spicoli in Fast Times at Ridgemont High.

Literature

Lucas Cott in Johanna Hurwitz's Class Clown. Eventually he grows out of this role and his Foe Yay Slap Slap Kiss Toy Ship relationship with Cricket Kaufman becomes friendly as he demonstrates how smart he really is.
Louis Sachar's Dogs Don't Tell Jokes is about a class clown who learns to take comedy more seriously, paradoxical as that sounds.
The Weasley twins (and their friend Lee Jordan) in Harry Potter. The twins actually make a profitable career out of this by manufacturing magic sweets, joke items and fireworks.

Live Action Television

An episode of CSI had a much darker take; the class clown was also the school bully who largely got away with being a jerk to everyone by being this. He's shot by the school's counselor, who was caught up in a school shooting once and wanted to stop him before one of his victims stopped seeing the funny side of it and snapped.
Xander in Buffy the Vampire Slayer. He hoped to be named official class clown at graduation but it went to another student who Xander dismissed as a mere 'prop comic'.
Ned's Declassified School Survival Guide had an episode about this, with the plot being that the up-to-this-point-unseen class clown character is leaving. As a Class Clown is needed to avoid the students falling into depression, they seek someone to replace them. Gordy reveals he was once a class clown when he was younger, and tries to help Ned take on this role (As Ned was just unable to be funny by himself). Eventually a Deadpan Snarker is picked to take their place, who was unwilling as he didn't want to get in trouble.
Willie Oleson on Little House On the Prairie was in the corner so often for goofing off, that when he and Laura both got sent to the corner in an episode, he told Laura to get out of "his" corner.
Bulk and Skull from Mighty Morphin Power Rangers were officially bullies but were never shown actually bullying anyone (except in the unaired pilot) and behaved much more like class clowns, trying to show off and ending up slapstick Butt Monkeys of the show and their zany antics would often land them in detention. However, in season three they join the junior police force and go throug various jobs all the way into Lost Galaxy.

Stand Up Comedy

One of George Carlin's earlier routines is all about this.

Web Comics

In Max Overacts the main character Max thinks the whole world is a stage, and sees his 3rd grade class as his audience. Results are predictable.

Web Original

Subverted by The Nostalgia Critic. He acted like a monkey in eighth grade and was pitied highly for it, as well as bullied for that and other things.

Western Animation

An episode of The Simpsons had Homer and Marge go back to their old high school reunion. The former class clown was the one handing out awards.
- Bart is sometimes portrayed this way, too. In one episode, he even expresses disdain about this role:

"The whole class turned to me, as if waiting for me to make a joke, and that's when I realised it; I'm the class clown, and it sickens me."

Buster from Arthur.
Carlos on The Magic School Bus
Similarly to the comic example, Nightcrawler and Iceman (and by extension, most of the new recruits) fall under this in X-Men Evolution.
T.J. Detweiler from Recess, though he has a lot of respect from most of the students, and Miss Grotke finds most of his antics charming.