Good idea!

thanks :)

When you wrote "whacks cake with it" that was mean i like little kitties like cake! that's why my username is kitten queen!

D: no no no! i did not mean any offense to kittens of any sort! kittens are the best! i was just....and marshall lee.......i.......im sorry *tries to hug*

how about stuff that marceline says but in boyish way

Oh, and how about:

(Fionna cries after listening to Marshall Lee's mournful "Onion Rings" song)
ML: Huh? Oh, GREAT. *grunts in heavy sarcasm upon seeing Fionna cry* Jeez, Fionna, you ruined my beat! So NOT COOL.

Fionna *sniffs*: I-I'm sorry.... It's just that you seem to...sing so sadly 'bout your mom. Marshall Lee, why don't you visit her...or, y'know, see her?

ML *looks away*: Fi, it's not worth it visiting her. Not only are there a LOT of problems between us, she's in the Nightosphere. And you won't expect to find that anywhere. At least NOT HERE.

Fionna *hatches up an idea*: Tell me, Lee. How DO you get to the Nightosphere?

...Okay, I'm meaning to write more, but it will take up a LOT of space. (Actually, I'm planning to make this a genderbent version of the episode "It came from Nightosphere" in fanfiction.)
Well, that's a few lines, though I'm seriously debating whether I SHOULD write the story or not.

...In second thought, maybe I WILL. "It came from Nightosphere" is one of my favorites!

*BTW: Picture below [credits to deviantart.com]