The annoying behavior exhibited by people, which inevitably results in a chick not getting laid. Clit blocking can come in many forms, but typically has an element of someone dissuading a man from engaging in sexual activity with a woman.
She clit blocked me last night! He was going to let me sit on his face, but then she came along and ruined it by demanding that I take her home immediately. Ugh, what a clit blocker!