"Brain Drain", because Brainiac 5 minus proper functioning is way funnier than it's really supposed to be.
Bouncing Boy screaming like a girl.
How about when Lex Luthor's great-great-great-granddaughter sticks her tounge out at Superman, because he dumped her.
Phantom Girl acting like a stereotypical hick to mock Superman when he pulls the Adorkable farmboy thing is much funnier than it should be, the look on her face sells it afterwards:
Phantom Girl: *acting like a Deep Souther sarcastically* "Aw shucks, ma'am. I ain't never met nobody! Uh-huh! Uh-huh!" *grins at Superman smugly*
Lightning Lad's greatest fear? A little doll!
In Unnatural Alliances:
Imperiex: I believe you have have something I want.
Star Boy: What, Brainy's tuna salad recipe?
In one episode, Chameleon Boy pretends to be Persuader.
Chameleon Boy/Persuader: OW! That hurt! Superman: Sorry.
Lightning Lad: This energy cloud has brought us near the planet where my brother and I were infused with our powers ten years ago. ...It's also where we lost our sister, Ayla. Kell-El:...You're not going to start crying, are you? Lightning Lad:(continues talking as if he didn't hear him)
Also, when Energy cloud Ayla is begins singing the nursery rhyme:
Superman: THE CLOUD IS SINGING?! Bouncing Boy: Creepy.
In "Timber Wolf":
Bouncing Boy: Don't leave the hangar, huh? I can see why.
Brainiac 5: I assume we'll be snooping?
Bouncing Boy: Oh yeah.
Timber Wolf and Star Boy messing around during one of the Legion meetings in "In Your Dreams".