Not Usopp, he has one helluva big nose, pointy too that'd hurt to punch.
Not Franky because he has a metal nose, and punching that would hurt.
Not Robin & Nami, because they're girls and I'm very chivalrous to kind ladies.
Not Luffy, because your fist would go into his face, and rubber-ness would ensue.
Not Sanji, because he's cool. Same with Zoro, plus he carries 3 blades, man.
Not Chopper, he's dead on, unless of course he went Monster Point &
tried to attack you of course, or maybe in full human mode, if he was angry.
I'd punch Brook, it'd hurt like hell, since he's made of bones, but I'd tell
him to stop acting so stupid & swing for him.
I'd punch Don Krieg in the face. And Crocodile, even though he'd be pretty intimidating.
People like Arlong & Morgan would be contenders, but they have f***ed up faces that'd hurt
like hell to punch.