Because some of the world's biggest music stars are skipping vacations to make movies, that's why. It seems these overworked megastars, like everyone from your 12-year-old niece to the mailman, really want to act. And though this might seem like a good idea to some, the unfortunates who mistakenly wandered into the path of Mariah Carey's Glitter, Britney Spears' Crossroads or Madonna's Swept Away know that this is often a grave error.

Not that musicians can't act; some can. Whitney Houston stretched her acting muscles to portray a diva in The Bodyguard, and Eminem immersed himself in the role of a white rapper for his much anticipated 8 Mile. But for every rare Frank Sinatra, Barbra Streisand and Mark Wahlberg--singers who actually built a new career as actors--there are dozens of Vanilla Ices who sink both careers with an ill-advised acting gig. (And don't even get us started on the crimes committed by actors who just want to sing!)

So, take this fun new quiz that looks at some notable acting failures--and occasional successes--involving your favorite musicians.