The first, and only, time I've received hate mail was a very long time ago.
I was in Free Roam and was riding around in a stagecoach. I felt the urge to arm the cannons at El Presidio and blow some people up so I road out there. As soon as I got to the gates another player joined the session on the nearby hill. I didn't open fire on him because I never shoot people in Free Roam unless shot at first (or to help out people being ganged up on). He ran into the fort while I stayed on the stagecoach. I offered to give him a lift somewhere but instead was shot in the face. I chalked it up to him being a noob and didn't think anything of it. Then he shot the horses pulling the stagecoach, then shot me again. I then went all out on him, went back into the fort, and proceeded to blow him up with the cannons.
He finally left the session and a few minutes later I got a message saying,
"fuk u cheeser"