When you are sitting in the stall of a public bathroom and somebody walks in, prohibiting you from pooping, as you previously were or might have been about to.
A frustrating period of time where you are having either lasting constipation or are just all around not satisfied with the size. Especially when you can feel it coming but just can't seem to follow through. (Lasts from 2-5 days)
(Dale): After that chef boyardi chugging contest, I have been in the biggest Dump Slump
(Keith): Wah Wah Wahhhhhh