I very rarely turn a movie off, especially if it's Oscar-nominated and critically acclaimed. Last night, however, Y Tu Mama Tambien achieved that status with me. There was so much sex in the movie, and talk of sex ... I kept waiting for it to actually get to the plot. After half-watching for about 40 minutes, though, I gave up and turned it off. If it takes nearly half the movie for you to figure out the plot (if it ever gets there ... I don't know), and you're miserable getting to that point, it's not worth watching.
I wouldn't recommend Y Tu Mama Tambien.