Verb. To procrastinate, to be incredibly lazy, not working when you should do it. Especially, doing anything but working, and eventually finding any stupid excuse to explain the lack of finished work. It's an irregular verb: to mustang, mustangued, mustangued.
One similar word in definition is " to roy": to roy, royed, royed.
The colonel has mustangued all day long, he's so going to get shot.