(n.) Mack mack is a jibberish phrase similar to "yada yada", and is used when imitating someone's speech in a malevolent manner. It is commonly used when interrupting the speech of someone who is being annoying, offensive, or boring.
Person #1: Hey babe, what did you do today?
Person #2: Well i did YOUR laundry, I vacuumed, because YOU wont, I did the dishes, ...!!" etc.
Person #1: "Mack mack mack!"