Rectalgia is a medical term meaning a pain in the rectum. You can see where this is going, it can be usefully applied to people who are a pain in the arse, you know the WOSPs, Malcolms and fuckwits of the world. See also pygalgia.
To stay home from work or school due to the highprobability that a torrent of liquid awfulness will be expelled from your bowels involuntarily and without warning.