It's usually (or was, years ago) used in the context of the "kino ladder," which is the idea of increasingly intimate physical contact starting with like, shoulders or handshakes and progressing through legs and backs and hands and eventually each other's taints or something. It makes sense and is something most people intuitively do as they grow closer to someone; it's even good advice when two people have a mismatch between how they feel about each other and their typical physical contact. But it's stupid and creepy if you try to climb it like a psychopath.