Zac Efron and Robert De Niro's new "Dirty Grandpa" got an R rating "for crude sexual content throughout, graphic nudity, and for language and drug use." Of course, if you're inclined to go see it, those are all selling points.

That's sort of the point, after all, of the R-rated comedy: to see just how far the movie can go in creating gags that push past the limits of taste and propriety without getting an even harsher NC-17 rating. Over the past 40 years, the genre has proved we're willing to snicker at some pretty nasty and twisted stuff. Here are some of the R-rated comedies that still make us laugh, even after years of funny filmmakers pushing the envelope.