jitter shitter 

Someone who inexplicably feels the need to poop whenever they are nervous.

Bob is always in the bathroom before a test; he's a total jitter shitter.

jitter shitter by Brianbratcher February 14, 2015

Shitter Jitters 

A feeling of fright or uneasiness about defecating in a public or foreign bathroom.

Dave: Why is John so pale and nervous?

Walter: Oh, he just has a bad case of the Shitter Jitters because we're at a party and he has to drop a deuce.

Shitter Jitters by Silver Panther April 27, 2010