In all honesty I have seen someone trying to game on of my friends, as it happens I knew the guy and he was, to be polite a total douche bag. So when my friend went to the bar I walked up to him and started having a friendly conversation with him, he instantly started giving me shit about this girl, he must have not known that she was my friend. Anyway, at the point, without her being there I exposed him, told him I knew what he was doing etc. At this point he put his arm around me tried to act friendly and said "why would you want to cock block me?", my reply was.. "because you're a cock" anyway I knew she was coming back, said hello to her and walked off, after about half hour, she walked up to me apparently the guy made some excuse and had to leave. At the time I did feel bad, but I would have felt worse if i had let him pick her up, so it had to be done. other than that I've never seen/overheard someone purposely gaming someone while i've been out.

Cube