Slang from Wales: When you think someone is lying you'd use it to show that you know/think they're lying. Also this is used with a gesture where you brush your hand up from the neck to the tip of the chin.
First personpossessive pronoun, informal signifying ignoble attachment to an object deemed unworthy of general approval, esp. a political object, & employed to ridicule an opponent's ideological obsession.
Steve: Hey Jerry did you hear about Mrs. Smith?
Jerry: Yeah, I heard she left her leash at her house when she took her dog for a walk. What a fucking muh.
Steve: Yeah, she really is a fucking muh.