Butt of a joke? (14)
(Other definitions for stooge that I've seen before include "Yes-man" , "Comedian's feed" , "Toes go wrong for the scapegoat" , "lackey" , "Butt of a comic's jokes" .)
(Other definitions for whoopee cushion that I've seen before include "source of juvenile amusement" , "Inflatable source of much mirth?" .)