"Sixty Years of Bad Sex" joke

An elderly couple were sitting on their front porch one evening, when the wife picks up her cane and whaps her husband across the shins.

"All right woman! What the hell was that for?" he yells.

"That's for 60 years of bad sex." she replies.

A few minutes later, the husband picks up his cane and whaps his wife across the shins.

"Ow!!" she yells. "What the hell was THAT for??"

The husband looks at her and says, "That's for knowing the difference."