I'd offer to do it because I'm a nice guy, but I'd hope that if the girl was offended or wanted to do it herself she'd say something instead of just making us both feel wierd about it. And if she didn't happen to know how the piece worked, I wouldn't do it for her - I'd show her how to use it so she can feel like a more confident smoker. But it's usually obvious who knows how to smoke and who doesn't - my cousin is dating the sweetest girl, but she can hit like a pro. And before anyone takes it as sexism, note that I'd do the same thing for a dude who's a novice too.

It feels nice to do nice things for nice people.

EDIT: Post 429! I wasn't paying attention, guess I missed 420.