(in the car listening to "Puff the Magic Dragon")

GREG FOCKER: Who'd have thought it wasn't about a dragon.

JACK BYRNES: Huh?

GREG FOCKER: Well some people think that 'to puff the magic dragon' means to... puff... smoke... a marijuana cigarette.

JACK BYRNES: Puff is just the name of the boy's magical dragon... You a pothead, Focker?

GREG FOCKER: No, I pass on grass always. Well not always.

JACK BYRNES: Yes or no?

GREG FOCKER: No, um, yes, um...

(Movie: Meet the Parents)
 

"to puff the magic dragon" not only means to smoke m... it could also mean smoke heroin (crack) or other plant derivatives. Just FYI