^fairly often, and I'm usually on with them, unfortunately ;)
I'd have to say arena servers. They piss the hell out of me cos they are just giant spawn camp maps, with smg noobs everywhere. Zero skill, and 99% chance of getting spammed by smg fire as soon as you leave the spawnpoint.
Or komrades server, when a lot of them are on. I can hold my own against a couple of them, sometimes, but they just squad the shit out of you. Usually no on on the other team tries to squad, or does it poorly, while the kommies do it flawlessly, you kill a couple, lose some health, then two jump out of nowhere and kill you while you are weak. I kill two, then one spawns behind me while I'm facing a couple of others. Impossible.