Why do men find it so difficult to solve puzzles after taking Viagra?
Because they just keep getting harder and harder!
Alright listen up, nimrod! This joke is funny 'cause it uses a double meaning. Viagra makes a dude's pecker hard, and the joke implies the puzzles are also gettin' harder, ya get it? You probably need Viagra to get your brain up and running, I bet you shop at K-Mart.