A novelty sex-toy created by Fleshlight(tm), a manufacturer of male masturbation aids. It is a fake penis that is always limp (hence the name). Especially popular at bachelor/bachelorette parties, Mr. Limpy comes in several colors and sizes. It is famous for its stretch/launch-ability, as well as several other more practical uses (i.e. paperweight).
Hey, what did you just hit me with...<stares Mr. Limpy on the floor>...I'm so gonna kick your ass