Australian Handshake

When a man and woman contract their pelvic floor muscles during penis-in-vagina intercourse, causing the vagina to tighten and the penis to harden at the same time, thereby squeezing down on each other as if to perform a handshake. Called “Australian” because it occurs “down under”—beneath the belt.

Johnny: Tiffany and I just completed our business transaction with an Australian Handshake!
Ted: Why was it an Australian Handshake?
Johnny: Because she was a prostitute.