Green’s Dictionary of Slang

dumptruck v.

[dump v. (9); the image of losing control of one’s bowels + pun]

(US prison) to fail through a lack of nerve and courage, rather than through actual physical inadequacy.

[US]Bentley & Corbett Prison Sl. 93: Dump Trucked When a person fails at something because he was nervous and apprehensive about the outcome .