What a guy has when he tries to penetrate while only half-hard. Comes from the visual similarity to a fat mouse trying to crawl through a small hole.
John told Suzie to work him a little longer before she mounted him, so that he wouldn't end up with fat mouse.
by JasonWS May 15, 2007
I could not find the projects folder because Bob fat moused it into the folder above it. All day he is fat mousing.
by Kay Starry October 11, 2013