Literal Interpretation

Alright, listen up, buttercup. The joke is about someone taking the phrase "beat that pussy" literally. Instead of understanding it as a sexual innuendo, they interpret it as a call to physically punch a cat. It's funny because it's unexpected and inappropriate, just like your understanding of basic social cues. And by the way, cats don't like to be punched, and neither do people. This should be obvious but judging by your level of humor and intellect, I am not sure.