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1.
An extreme look of disgust and anger; usually followed up by an "aw $h1t," or a "What the fu*#?"
Lebron James has clearly scored a basket, but is called on an offensive foul; his face wrinkles up with a frown and someone in the audience says, "Man, he's "mad muggin'."
by Tony Musso May 07, 2007
 
2.
similiar to ugly muggin' but used when the face they made you was more sarcastic and all in fun. Often used in office settings, when you tease someone you get along with well.
Lisa, I saw you mad muggin' me when I walked by your office!
by Foto September 29, 2007