Rated NP for No Parents because of a curious obsession with imaginative descriptions of female parts, and extended awkward trying-to-have-sex-and-failing scenes. (This will become a theme in this list.)
Good luck trying to get through this one without pausing every sixty seconds for a Q&A session about exactly what is going on. If you accept the challenge, go ahead and write "I don't know, let's watch the movie and find out!" on a piece of paper to hold up instead.
Paul Rudd's psyching-himself-up-for-sex mirror moment may be one of the funniest scenes ever put to film, but it's not for extended family consumption. (But for real: the above is one of the funniest scenes of all time. Use headphones.)
Possibly the first mainstream comedy in history that could feasibly be too gross for a fifteen-year-old boy. Resist the impulse to think the R rating is for language and nudity - this movie crosses lines that probably have never occurred to you and aren't in the trailer. This entire list was inspired by this movie. Beware! "Accidentally" break the DVD in half if you have to!