shit pang
That feeling you get in the nether regions when you feel the need to take a crap. Could be a clenching of the sphincter, or a gurgling of the bowels.
If you don't get to a restroom when you feel the shit pang coming on, you'll be backed up for the rest of the day. Alternatively, "I just felt a shit pang, gotta go drop the kids off at the pool.