oh man...I have like 2000 faves! But off the top of my head:
REESE: Malcolm, I live in a world of ''what the hell''s.
(I think it's from Malcolm Visits College.)
MALCOLM: Dewey. The coolest person in that class..was me.
DEWEY: Okay, I'll do it!
(Dewey's Special Class)
REESE: (holding a hammer) Then I played with Dewey's GameBoy...
(Experiment)
MALCOLM: (showing off his newly pierced tongue) And you know why I did this? Neither do I.
(Ida's Boyfriend)
STEVIE: Can't feel...my legs.
MALCOLM: ...That's not funny.
(Sleepover)
STEVIE: Good...game.
MALCOLM: This...sucks.
STEVIE: You...mocking me?
MALCOLM: No...tired.
(Rollerskates)
MALCOLM: (to Stevie) So, what can you do? I mean, what d'you wanna do?
(Pilot)
CAROLINE: Where's my credit card?.
REESE: It fell out of your wallet.
CAROLINE: How did that happen, it was...
REESE: Come on, let's go.
(Home Alone 4)
FRANCIS: Guys, I appreciate your sentiment...but they're not going to decide my whole future based on how I act on one weekend. It's too arbituary, it's...unreasonable.
MALCOLM: It's Mom.
FRANCIS: Okay let's clean up.
(Home Alone 4)
MALCOLM: Can I have some?
STEVIE: Can't. It's a...prescription...sandwich.
MALCOLM: Prescription sandwich? Stevie, that's not even a good lie! If you don't want to share, just say so.
STEVIE: Don't want...to share.
(Francis Escapes)
REESE: He's cute. I hate him for being cute.
(Convention)
HERBIE: I didn't want to tell you this, Dewey, but if you don't buy me... You'll die.
(Hmm. This is the first one I'm not sure on. Typical. Shame, maybe?)
And of course the two from my signature
(I've done all these from memory so they could be misquoted or I wrote the wrong episode. If so, sorry!)