The worst is at the start of the game. Map loads, 1 guy joins humans and 2 join aliens, then there are 10 spectators waiting there. 3/4 of the time, the aliens won last round and everyone just wants to join the winning team. Then you, who legitimately want to play aliens, gets stuck there. Usually you end up being the courteous player who caves and joins humans, watching a guy join aliens a split-second later due to a team join bind.
(note: happens equally for both teams, had to use one as an example though)