A full mustache or 'stache worn in fu manchu style with a goatee, with or without a patch, in the style of former St. Louis Cardinals home-run hitter Mark McGwire.
I got tired of foolin' with a full beard, so I shaved off the sides and turned it into a McGwire.
Originating from old Irish, the McGwire was the village man who always thought of himself as big and grand, when in reality it was much talk. The McGwire would always be hated upon by other villagers.
"omg that guys is such a McGwire"