PC "X" was just really nasty to me in game! Have I done something to annoy this player?
It's very unlikely that you have. It's important not to confuse In Character and Out Of Character behaviour. Players on Thain are generally a friendly and welcoming lot; however, their characters may not be!
If you do feel that someone is making you feel uncomfortable Out Of Character, the first thing you can do is approach them about it and discuss it with them. If this solves nothing, please let a DM know about the problem.