Although it will never happen, i think it would be funny to imagine who in One Piece would partake in the sweet leaf and how they would act. Considering how goofy some of the characters are, i think there would be a lot of funny moments.
Zoro- He may do it to relax for his naps. He might be a vulture though, always sneaking up on whoever had it and "cut" into the rotation. Only problem is Zoro already has a bad sense of direction, he might get lost forever.
Sanji- He already smokes like a chimney, this would just be "green tobacco" to him, plus he can cook up some great munchy food.
Luffy- I think he would try it, but i think the crew would stop him from doing it too much, Sanji has to cook a ton of food anyway and if Luffy had the munchies, imagine how much food he would eat then! Having rubber lungs means that Luffy can take monsterous hits.
Chopper- Hey, it has it medical uses too.
Franky- Not sure, he runs off cola, but man could he build some awesome stuff to smoke it out of.
Brooke- He's a musican, it's almost required. Even with no lungs, i think he would still enjoy it.
Nami-Maybe once in awhile by herself.
Usopp-Totally. "This one time, i defeated like a whole army of marines with just one shot." He's already a pacifist, this would just reinforce it.
Robin- Nah, she's a smart girl, but i think she would find it funny.
Smoker- Obviously. The only guy who could use it to his advantage. You think those are cigars?
Ace- More then likely, he would never need a lighter.
Admiral Kizaru- He talks real slow as it is, seems he already does it.
Trafalgar Law- Dude looks stoned anyways " hey man, i need a talking kung-fu bear in my crew…"
Pappug- He's already wearing the hat for it. Hooking the Strawhats up with the "seaWeed".
That's all i can think of for the moment. So have a laugh and share your thoughts on who would smoke and what funny moments may come from it. Oh, and if anyone can make any photoshoped pictures of characters doing it, i would love to see them.