It's hard to get them fired from one complaint but if the dean or chair receives numerous complaints then something has to be done about it whether it be getting written up or put on probation is at their discretion though. I worked in a college and saw many horrible professors, hell we had one still teaching Cable LAN which hasn't been around since the late 70's early 80's and he was there for a year before he was fired. If they have tenure its even more difficult.