Good GMing requires you act like a mature, rational adult. Yes, we know
everyone considers themselves such already. Nevertheless, we're saying it
because it needs saying. After all, even the most rational of individuals
has "down" times where they may unfortunately act like brats.
This category is different from dealing with problem players because
it's for you, the GM. We expect people here to behave responsibly,
act like adults, and contribute to the enjoyment of the group. You'll
want to be sure you avoid behaving like a petty tyrant in-game; wasting
time with constant self-justification/explanation; constant whining or
playing the martyr; insisting things constantly go your way; or playing
when bored, tired, or sick.
Catching yourself doing this once or twice is forgivable. However,
if you find yourself doing any of these repeatedly, you might want to
seriously consider if you're having fun GMing any more.