Hitmarker headshots with bolt action.
Noobtubes.
Most of the killstreaks..(If you're not the one calling it in)

aimbots.

airblasting pyros

100% of the time its a shot in the shoulder or somewhere else

if there using the noobtubes play a strategic role, then i don't get mad
only if there constantly using it as a primary weapon i hate that

killstreaks in general because there WAY too OP, i liked the old ones where it was fixed at radar, airstrike, and helicopter

also quickscopers who think there so pro because they use a sniper rifle