A "friend" of mine. My boyfriend and I often hold LANs at our house, and, knowing that this "friend" enjoyed Diablo 2, we invited him to one of them. It was a lovely summer evening, so before we all got down to gaming, we started up a BBQ for him and the other 3 or 4 guests.
Our hopes that he would enjoy his evening and we ours began to go downhill when the "friend" announced he was sure hoping we'd start gaming soon, as he didn't have all evening. He then didn't speak throughout dinner, but spent it texting people on his mobile.
Once we got to the computers, things simply went downhill. Suffice to say, he accused us of cheating for using a mod (all players had previously completed the game on normal before) and then spent the game running around as far away from the main group as possible. No fun, no banter, and when he left, he didn't say thank you.
We never invited him back.