plural form of Mug Nug.Short for Muggle Nuggets. A muggle nugget would be someones testicles that are NOT magic, thus making them Muggle Nuggets.
Tom: He almost hit me in the Magic Nuggets!
Jack: You don't have any Magic Nuggets you just have a pair of Muggle Nuggets*.
* In this sentence the shortened form, Mug Nugs, could have taken the place of Muggle Nuggets.