It's pure torture to watch De Niro here

WHEN a movie's main premise is based on the crude antics of a horny senior citizen and his desire to have sex with a college girl, you might justifiably expect it to be just another dumb comedy on the lower end of the juvenile scale - predictably risqué and easily forgettable, along the lines of say, Dumb and Dumber 2, Deuce Bigalow: European Gigolo and yes, those Little Fockers.

You'd be wrong, though. It's much worse than that.

It's only January but Dirty Grandpa is already a frontrunner for (dis)honours as worst movie of the year. And in the surest sign yet that the movie apocalypse is upon us, it stars Robert De Niro, without question one of the finest actors of his generation. His riveting performances as an ambitious young mobster (The Godfather Part II, 1974), a psychotic New York cabbie (Taxi Driver, 1976) and a brutally self-destructive bo…