This is in reference to doing something that is self-destructive. Farting in the shower does nothing but make your life unpleasant.
Bucky: "Hey! Did you hear about Andy? "
Lewis: "Nope. Is he in the clink?"
Bucky: "Nah, he asked out Marcia when Scott was right there. Totally farting in the shower. Scott slammed him into the wall and then spit on him. A real dick move. It's like he wants to ruin his own life more than we do..."