Oddly enough, Medic. Not that there's anything wrong with a class that's supposed to heal their teammates but it's the vast majority of people who play or even main Medic who are completely senseless. Most of them pocket Heavies and pay no notice of the rest of their team, sometimes they waste time by trying to use their crossbow to heal you at close range rather than their medigun, they tend to make the most stereotypes of other players such as the "I don't heal Scouts because they steal medkits" (and I've witnessed several cases where a Medic pocketing someone has taken a medkit while a burning player needed it but then refuses to heal them) and finally, they're rarely team players.
I've certainly met some decent Medic players but they're usually very rare and the others are almost always dickheads.
I've certainly met some decent Medic players but they're usually very rare and the others are almost always dickheads.