-People that don't know what to do/how to build champs. I had a guy who FP nasus, built a randuins and sunfire with no CDR, then complained about how bad we were doing when he had 300 stacks at 30 mins.
-Supports that don't get a sighstone. Idc what champ you pick, build a damn sighstone, no matter what. Usually tends to happen on AP supports like zilean and nidalee. So damn annoying.