-W+M1 Pyros (When I mean that, I mean nothing but that).
-Demos who keep laying stickies near the spawn area.
-Demos who only use stickies.
-Other engis who keep building their stuff right beside yours.
-Medics who only heal heavies/demos/soldiers/pyros.
-Medics who only uber 1 specific class.
-Pyros with compression blast who
don't use it to extinguish players (especially burning medics).
-Trying to keep a sentry up while you're surrounded by many people (mostly spies sapping) and nobody will help you.
-Being killed right before being able to backstab someone.
-Being facestabbed (I got facestabbed in the vents in CTF_Turbine

).
-Pyro's laggy flamethrower that reaches you even though you're out of range.
-Stray crit rocket that pops out of nowhere and goes after me.
-Engis who don't set up teleporters.
I'll think of more later...as for now, I'll just think happy thoughts so the game doesn't seem so depressing, haha.