I've got a new one: People who don't speak the language and/or don't heed some good advice.
So, Bioticslab, hard, long, 6 people, mix of perks from 3-5, and with me at 6 Support. One of the players is a guy with a [THAI] tag in his name and 240 ping. I'm mostly talking through mic with some text here and there.
Scrake appears: "Let me take care of him. Take out the little guys around him." The others do as I request and mop up trash as I go up to do the good old hunting shotgun tactic on chainsaw dudes. My reasoning is that I'll save the Supports AA12 ammo for the mobs (which I bought for them; they were grateful, which makes me a happy gamer. I love helping people). As I move up to melee range of the Scrake, [THAI] moves up and spams the Scrake with his AA12. Scrake un-flinches, and I get a third of my armor ripped off. Rinse and repeat until I have no armor and the only thing keeping me on my feet is the dutiful Medic in the back.
Fleshpounds: "Back and up spam grenades!" I follow my own advice... but [THAI] runs up just as I toss my second nade and... you guessed it, starts to spam the FP with the AA12. I get knocked to 40HP and no armor and the FP takes out [THAI]. We manage to kill the FP, but it was really dicey there for a moment. Managed to live through the round.
Patriarch: "Pipe spam!" (I mean, why not. Haven't done that in a while). So we pipe spam the double doors (in the middle floor lab area) and I tell them not to weld so Kevin won't detonate the pipes. And [THAI]... welds just as Kevin closes in. One "ONE IN THE PIPE" later, all the pipes are knocked out, and Kevin collects us as science experiments.
All the while I'm using my mic and the text chat to try to convey to [THAI] that he was going to get us killed.
Gah. It's been a long, long time since I've had a frustrating game.