Actually I have another suggestion, one I've been meaning to post for some time:
So you're in peaceful, meaning you can't hurt the dude standing in front of you (or maybe he's in peaceful..... anyway.......)
When you punch/kick someone, it should knock them back a short space (even if you're in peaceful)...... and if they're not in a dungeon, it should freeze them for like a half-second. This will allow peaceful players to release aggression on each other
while also preventing someone from blocking another player.