The whole etiquette thing is a farce and needs to be thrown out.
It's one thing kicking the ball out when one of your guys needs attention, but you shouldn't be expected to do it when it's one of the other team. It encourages play-acting and feigning injury. If the ref deems the injury to be serious enough (typically a head injury) he alone should stop it. Otherwise, play on and to the whistle. Always.