“Dirty Grandpa” (*1/2 out of four) was a crude, stupid and proud-of-it comedy starring Robert De Niro as a perverted senior citizen on a road trip with his uptight grandson (Zack Efron) to Florida where he is about to be married. Some nasty laughs in the opening half-hour are soon dissipated as film becomes endlessly raunchy and dumb. Seeing De Niro play such a wacky character eventually proves tiresome, just like the film itself. Film makes fun of homosexuals, blacks, and of course senior citizens in equal measure so no one feels left out of the party. Watch “Bad Grandpa” instead.