As many others have said, tanks are the integral part of the group. Every ounce of weight rests on their shoulders. If you forget to pop 1 cooldown and die because of it, everyone knows. If you lose aggro to a DPS that doesn't care about threat meters, its not his fault, it's the crappy tanks fault. If you don't pull monsters in the most perfect form every time, people bicker and moan. If you aren't on top of your game 100% of the time, people take notice, and they complain.

Tanks are by far the most stressful jobs out there and are sorely unappreciated. After months of gritting your teeth through everything, you tend to become short tempered. Some people don't, most people do.

I personally feel that if people expect me to play at 100% all of the time, then it is just as fair for me to expect it of them. If I'm playing with friends and I know I'm in a relaxed environment, entirely different story. But I swear to God if one of you pubs pulls aggro...