The breather episode "Revved Up" has several. Starfire and Raven pretending to be the evil "Dr. Mumgam" and "Henchy" with Starfire failing at it, and then the wrecked T-car going through a tunnel and emerging from it as Cyborg on a single axle with Beast Boy as a horse on the reins.
From "Every Dog Has His Day", Starfire & Raven are focusing on a crystal ball, with Raven describing how they:
Raven: Need peace, and absolute-"
(Beast Boy's head appears warped, on/in the ball): DUDES!!
(the girls scream and clamp onto each other)
What, no love for the episode starring Robin's inter-dimensional counterpart, Larry? When they wind up breakingreality, Beast Boy loses his mouth, and steals Raven's so that he can speak. Then she steals Cyborg's...then he steals Starfire's. One must wonder how the voice actors avoided cracking up, especially Khary Payton having to imitate Raven's deadpan-ness.
Or when Raven sees flowers walking around in the new colorful world she says "This is bad." She then sees Beast Boy without a mouth and says "Okay...so it's not all bad."
Also would be Larry's excitement over his new moniker, saying his name over and over again while doing er...interesting things with the titans.
Starfire: Disturbing yet magnificent! I never knew wearing a cape could be so much fun! It is wonderful to be Robin!
"Did you NOT see the movie? When you split up the monster hunts you down one by one. Starting with the good-looking comic relief guy...ME! And I'm probably delicious!"
"I'd like to go to jail now, please."
The entirety of "Lightspeed".
"I paid for that!"
Another one: While Robin is away seeking training, the other Titans raid his room and start wearing his spare costumes, till Raven walks in, and says, "This is just disturbing" - after which she of course joins in, only to have Robin himself walk in...it just really works.
The beginning of "The Lost Episode" has Robin and Cyborg playing a video game, Starfire cooking alien food, and Raven reading her book when Beast Boy comes in with a boombox turned up loud and decides to crank it up more by plugging it into the main power grid, which causes everything to go haywire and the tower loses power and everything goes dark. In great Steve Urkel fashion, Beast Boy says "Did I do that?"
From Revolution: "I'm American!" "You're welcome."
Commentator:Oh, hoho, that had to hurt! Let's look at the replay, Chuck! You know, I'm not sure why a Teen Titan is on the field at the Championship game, but this is just a great defensive play by the Steel City Tigers.
Starfire in the Dr. Suess-esque cartoon, rhyming along with the characters.
Pelican: Oh have you seen my hippo? He hides and I must seek!
Starfire: I cannot play, please do you know a strange man named Control Freak? He is big, not tall, and nasty, and known for causing strife. He escaped into the TV-
Beast Boy(while being chased by a laser shooting robot): HEY STAR, RUN FOR YOUR LIFE!
Robin: -REALLY makes a forced, wide smile- -cracking sound effects- Maybe.
Starfire makes the best faces in that episode. The best one comes when she's at the punch bowl and some poor sap makes the mistake of asking if she can move so he can get some punch. It has to be seen to be believed.
In "Transformation," as Beast Boy desperately waits to use the bathroom he is exposed to, among other things, Robin performing the classic garden hose gag, followed by a baffled Aside Glance. Then there's Cyborg pouring himself a glass of water from the sink. Shortly after we see Raven moving two rocks to let water pass mimicking the same gag but from a "female" perspective.
"L, M, N, O, PEEEEEE"!
"This is the greatest pie. In the history of pie."
Starfire: Oh, hello long-lost friend!! You remember me, yes?
Terra: Of course, Starfire. I still have bruises from the last time you hugged me.
Pretty much everything Beast Boy and Cyborg do in "Stranded," highlights being Beast Boy turning into a wookiee and Cyborg resigning to BB's inability to understand scientific terminology, telling him to "pull the red candy cane thingamozy."
From the same episode, we have the adorable little alien thingies that worship Raven, constantly going, "Shala!!" after repeating everything she says.
The Visual Pun of "SHE'S GONNA BLOW!" applying to an angry Starfire is enough to makes make people laugh their ass off.
Robin and Starfire have some of the best interactions.
Starfire: Robin, who is this girl? And why does she call you "poo"?
Robin's reactions to Starfire's line are hilarious.
Even in the depths of rage and jealousy, Starfire does not once break from her speech pattern:
"Odium! Scandal! Atrocity! These demands must not be met! -Snip- Out of his mind if he thinks you would even consider such a distasteful-!"
Mumbo calls for a lovely assistant from the audience and yanks Starfire down with a cane. He then assembles a "sawing-a-woman-in-half thin-model box" around Starfire. As he prepares to perform the "trick", he adds:
From "Crash", while Cyborg is driven mad and turned into an Extreme Omnivore by the Endzone Virus:
Cyborg: Oh, I know who you are- YOU'RE THE NASTY EGG PEOPLE THAT STOLE MY WAFFLES!!
Cyborg:(yelling at an ATM machine) You can keep your sprinkles! I NEED RASPBERRY FILLING! (punches the machine, which spits out a bunch of dollar bills into Cyborg's mouth)
Cyborg:(spits out the money) NO! NOT MACARONI!
Cyborg: I feel like I ate a tire... (belches up an actual tire)
The Endzone Virus mercilessly ribbing on Beast Boy's intelligence.
Starfire: Still, after all this, I wonder... What became of the Gizmo...?
(cut to the radio tower satellite dish, where a pile of Cyborg's virus-infested snot resides)
Gizmo:(still microscopic-sized, stuck in the snot pile, frantically swimming away from Endzone Virus cells in a mad front crawl) RAZZLE-FRAZZLE TITANS! CRUUUUUUUUUDD!!!
The entirety of the episode "Revolution."
Cyborg's line in "Cyborg the Barbarian" after finding out that he's been transported to 3,000 B.C.:
Cyborg: "Don't do anything, don't touch anything. Sci-fi rule number one: You start messing with the past, you end up with monkeys ruling in the future."
The Hive Five (Six) centric episode is pretty hilarious, what with the rampant immaturity of the non-Jinx members (yes, even Kid Wykkyd) such as:
Billy Numerous:Y'll wanna build a fort out of sofa cushions?!
On the DVD commentary bits "Know Your Villains" it lists each villain, who their "nemesis" is, and where they are currently. For some of the lighter villains this can get pretty hilarious, such as The Source is currently "Lunch", Mother Mae-Eye is currently "serving pie to the H.I.V.E Five", etc.
Remember when Killer Moth made an army of mutant moths and forced Robin to take his daughter to prom *cut to Robin avoiding Kitten* and he was like "NAAAH!", *cut to Starfire choking Kitten* and you were like "GRRR!", *cut to Robin in a light used for Corner of Woe (though he's not sulking)* and Robin was like "Shrr....", *cut to Cyborg, BB and Raven in Killer Moth's base* but then we found Killer Moth, *cut to Beast Boy* and I was like "DUUUDE!", *cut to Raven* and Raven was like "ZZZTT", *cut to Cyborg* and Cyborg was like "BOOYAH!", *cut to Killer Moth on the ground, beaten* and we kicked his butt...
"Masks": Red X got Beast Boy out of the way of a train just in time.
Beast Boy: Dude, did you just save me?
Red X: (kicks him aside)
The episode "Fractured" is one of the most bizarre episodes of the entire series, so naturally, it's absolutely hilarious.
The short where the Titans finally catch Red X and take of his mask - to reveal several masks, including Jason Todd, Speedy, Alfred, Batman, Slade, and finally, a bomb.
Beast Boy: I still think you're Jason Todd!
Cyborg's initiation into HIVE includes a pink dress and a unicycle.
Cyborg singing to himself is a strong contender for funniest moment of the series:
Cyborg:(Singing in tune with theTheme Song) When there's trouble, you know what to dooooo... CALL CYBORG! He can shoot a rocket from his shooooeeees... 'CAUSE HE'S CYBORG! Dananana somethin' like that! Uh-huh! Dananana big, fluffy cat! That right!