I had a player who actually tried to sneak Pun-Pun into my game. Problem was, nobody in our group was much of an optimizer, and I had no reason to suspect shenanigans. He told me he was playing a Kobold sorcerer, and I took this at face value (stupid me ). That was fun.

He was a massive optimizer in a game where nobody really optimized much beyond getting some minor synergies between classes. On top of that, he always argued over any rule that he didn't like. It didn't matter if it was RAW or RAI or a houserule or anything. If what I was doing wasn't beneficial to him, he'd argue. If I went against RAW, he'd use RAW against me. If I went with RAW or RAI and it was detrimental to him, he'd argue "That's stupid, the rules are wrong, it should be like this."

Very frustrating individual.