Why do women cock block?

It's probably not about you. Especially if the friend already has a boyfriend.

Might be a completely different situation, but I have one friend in particular who likes to drink more than most when we go out. And she gets. Well. Easy. Then is depressed and hates herself for weeks afterward, because she humiliates herself and leads guys on. Unfortunately that also means whoever is with her has to play blocker, whether we want to or not.

Then there's girls nights. Guys might not know this, but girls nights are often preceded by agreements beforehand. If one of us sees another being grinded on or aggressively pursued in a way that's not wanted, another is always there to step in on cue. And yes there's usually a subtle "save-me" cue arranged ahead of time, which is probably still less harsh than the alternative. We're going out to have fun, not hook up.

Other possibilities are she doesn't think you're good enough for her friend, which isn't for her to say or judge, but it happens. Or she feels like a third wheel per BQ89 which isn't fair either, but again, it happens.

Instead of going for the kiss, just get the girl's number. You can chat her up one-on-one later.

Well sometimes it means that we feel like the third wheel and try everything that we can to make it not seem that way. Or we might like you too and its making us jealous or uncomfortable to see you all over some other girl! =)