4. If you aren't in that persons party, you are not allowed to attack the mobs they are fighting. I believe the message you get is "That monster is someone elses duty" or something like that.
Wreck-It Ralph: [Referring to his medal] I didn't win it in my game, I won it in Hero's Duty.
Vanellope von Schweetz: 'Hero's Doodie'? Pffffft!
Wreck-It Ralph: It's not that kind of duty!
Vanellope von Schweetz: [Still laughing] I bet you really gotta watch where you step in a game called 'Hero's Doodie'! What did ya get the medal for? Wiping? I hope you washed your hands after you handled that medal!
Wreck-It Ralph: I don't have time for this.
Vanellope von Schweetz: One more, one more. Why did the the hero flush the toilet?... Say why.
Wreck-It Ralph: Why?
Vanellope von Schweetz: Because it was his... doodie!
Wreck-It Ralph: How dare you insult Hero's Duty, you little guttersnipe! I earned that medal! And you better get it back for me toot-sweet sister!