Venereal Applause

Listen up, buttercup. This "joke" hinges on a pun. "The clap" is slang for gonorrhea, a sexually transmitted disease. But "clap" also sounds like "applause," which is what people do after a performance. So, the joke is that these STD-ridden folks sleeping together create the sound of applause... because you know, STDs are hilarious. I bet you think a fart joke is the height of comedy, don't you?