A lot of the people here that are going "Fuck that bitch" clearly haven"t been out with their girlfriend with a bunch of friends. This is very common actually... girls will usually give you all their attention and be all lovey dovey when it"s just the two of you, but if you"re out at a public place like a bar, dinner, etc, don"t even expect that kind of attention, at least until they start getting drunk. From what I"ve gathered it really doesn"t seem to be something they do intentionally, it"s just how the social dynamic changes... they"re not crazy bitches out to cut you down (usually...).
No matter how much it pissed you off Heylel, you can"t ever do that in front of her friends. Ever. She has every right to be afraid of you, even if your intentions are harmless. For one thing, you had a physical outburst toward her. Doesn"t matter if it was a gentle pull or whatever... it sound like you pulled her pretty hard to get your point across. Secondly... it happened in front of her friends, which is even worse. You can"t embarrass her in front of her friends or any close social group in public pretty much ever. You can bet that people saw that and later on asked each other "What the fuck was going on there with that guy?" She knows this as well, and it"s probably quite humiliating. Anything physical like that is just a no no, as in, don"t ever do that or you risk the relationship, especially if it"s early on.
I"m not justifying what she did, or even saying you intentions were rotten. Despite all the people saying man up about the pinches, yea, they can fucking HURT (but I suspect their sarcasm is geared more toward what you did after). But it was certainly a mistake to do that in front of a group of 20 people. I"ve been in situations like that as well sometimes, you just have to voice your concerns later to her and make sure she understands it so it doesn"t happen again.