The best way to assert your dominance, you're too much of a badass to say "shut your mouth", or "shut up". shut mouth is a legendary term used by only the most epic of gamers.
1) Adj. Response when you are happy, but surprised or shocked by what was said.
2) Adj. Response to an insult. Often said by sassyafrican american women on Jerry Springer etc.
1) smarmy tv show host: you've just won a years supply of Snack Packs!
Fat guy: shut-your-mouth
2) Some chick: You stole my man? You dirty scank!
Sassy chick: You shut your mouth! He dont want you no more. MmmHmm (followed by clicking fingers from side to side)
Suppose you're with your grandma at her usual bing spot. One of the elderly spills his drink all over your back. You yell "Mother-" but catch your felf and say "Mother-shut-your-mouth". You are now the sweetest person for not cursing.