It's always the people who are most intolerant, who are the most intolerable.
It's always those most easily annoyed, who are in fact most annoying.
And it's always the most irritable, who are most irritating.
Think of the people you know who are most easily annoyed, or irritated. You'll find a certain symmetry.
It's a little like the way people always accuse others of their own faults: dumb people are always accusing others of being dumb. Liars are always accusing others of dishonesty. And so on.
Listen to someone talk about others long enough, and you'll know him.