Lets be honest, booing the players off the pitch at full time isn't that bad when they have put in a godawful performance like that. Its the abuse they get during the game that is out of order.
Personally, I don't boo players. They are not pantomime villains, and I am not a child. But if someone wants to show the players they weren't happy after the game, I dont have a problem with them booing. I much prefer to just walk out without clapping them off if I am not happy with the performance, but booing after the game is in no way as bad as hurling abuse/ironic cheers etc... during the game.