At a party, that one person that doesn't seem to know anyone except for you. They continually follow you around and insist on hanging out with you afterward. For the full effect, must start off nice, yet become incredible annoying.
A: "Dude, I got leeched by Anna last night."
B: "That sucks."
When someone eats out a girl while she's on her period.
Last night I went to a party and Emma told me that a ginger totally leeched some random hoe in the bathroom. DAT SHIT NASTAY.