I'd love to see what the "rude responses" were responses to, when marking mobs in dungeons is so ridiculously unnecessary. I'd probably have a few rude responses of my own to someone of your attitude, really sounds like you asked/insisted, maybe even repeatedly, that they mark things.

And people not attacking the same target rarely matters at all. As a good tank I'm concerned with holding hate on all targets, and that's easy enough to do that I could really care less what you attack first, and if/when I do think it'll matter, I'll follow the DPS's lead on what they're attacking, just cause.