I remember a very funny(or infuriating) example when I was playing my storm/electrical defender in my earlier days. The team was engaging a mob above and was taking them out nicely, but I fell down and a mob was about to attack me since I fell way to close. I rushed them with my hurricane, since they were in a very well enclosed room and locked them down, but the teams scrapper decided to rush to a mob by himself and started getting his butt kicked. He invariably ran for it and pulled the mob directly into my location, just open enough that I couldn't keep them closed together.
A few of the team got killed and the controller turned to me and said "Stop herding defender! Herding is for tankers!" and quit the team, blaming me for the mess even after I managed to fend off the extra mob that idiot scrapper pulled. In fact I think I had more moments of anti-knockback phobia on my storm defender and later my more successful storm corruptor that it got very annoying. I had another case where, in my days where I was really enjoying the debuffs, I had a dominator who hated me cause I called everyone in the team "guys"(it quickly turned out she was a sexist) when I asked how I was doing with my storm powers. I asked later and she said "right here" and quit.
I had another stupid moment here and there on my kin/energy defender. Ahem, "Stop knocking them around!". "Don't listen to Energetic, she's to addled with knockback!" Course it leaves me with the thought "Um, oook so your completely ignoring my multi-stacking fulcrum shift because of my knockback?" I even left a team once on a force field/energy defender because they were seriously knockback phobic, though they were also mad at the scrapper using shockwave.
I think the most annoying teams though were those that said they needed a healer when I was playing a defender or corruptor WITH that capability. I even told them I was on a kin and they were all "Its not enough!". I'm thinking "Um, excuse me? You guys suck so bad as to need someone else when I already got one of the most powerful heals out there?" They weren't good players anyways, one of them was an ice tanker who died constantly and the other was a fire tanker...ironicly the fire tanker was able to take care of himself, it still irked me he asked for that.
Lastly I can remember many trials where people DEMANDED everyone already be +3 before they entered, that included sadly even the earlier incarnate trials. I remember in guild wars with the HA rank "requirements", of which the only way to get those heroes ascent ranks was playing heroes ascent. Glad I only met a few teams going to the extreme of every trial demanding +3 on virtue, but it left me extremely insecure feeling that I'd have a very hard time getting later characters incarnate powers just because of the elitism of some people.