Players not knowing their characters' abilities
Players not paying attention to party planning during a session
Player A talking over player B when the GM is trying to talk to B
Players who continually "fight the world" - meaning, a GM gives you a world, and context. You should be able to make a character that fits, so don't make a Greek charioteer character in a Tolkienesque world.
GMs who frequently railroad the party. (Sometimes plot dictates actions, but I've played campaigns where "options" are presented, but only one is allowed. Over, and over.)