this is easy u have to just invent jokes about or said by the crew but not just take a random joke and change names or things like that try to think about some funny moment or speak from someone 
example:
Brooke: I just got a boner… HAHA SKULL JOKE IM ALL BONES!
…........right.
Anywho, two I done recently.
Robin: Ah....well....do you want the short version of the long version?
Chopper: Long Version
Robin: We are going to die.
Chopper: and.....and the short?
Robin: Bye.
only works in one of those 'certain death' bits though...
Luffy: GOMU GOMU PENORRR
@BLAzE:
Luffy: GOMU GOMU PENORRR
"GOMU GOMU NO PENORRR" you mean?
sorry just thought i'd be a jerk for a second
Bearsy: (Mumbles unintelligently) P-e–r-ona (and flails his arms around)
Perona: Zip it bearsy...U don't sound cute right now
Bearsy: (Mumbles unintelligently)
Perona turns and looks at him again as he stops
Perona: (Glares) I should have had that zipper placed over your mouth instead
of your back.
I swear this joke is ridiculous but thats the point its ridiculous that it's funny.
Bearsy: (Mumbles unintelligently) P-e–r-ona (and flails his arms around)
Perona: Zip it bearsy...U don't sound cute right now
Bearsy: (Mumbles unintelligently)
Perona turns and looks at him again as he stops
Perona: (Glares) I should have had that zipper placed over your mouth instead
of your back.I swear this joke is ridiculous but thats the point its ridiculous that it's funny.
Lets give Kumashi Fukurou's mouth. Maybe that'll work.
I think someone needs to eat a happle. <3Mah dA.Bombing for peace is like having sex for virginity.
Zorro:(jumping out of the flames at Little garden)
Nami&Vivi: O////O
Zorro: :wassat:
Nami&Vivi: (giggling)
Zorro: :getlost: (looks down)
Usopp: (giggles)
Zorro: :sick:
