QAS or Quivering Anus Syndrome. The stress related affliction when an individual's anus quivers uncontrollably immediately prior to or during a highly pressurized or nerve-wrecking situation. As the individual is under duress the anus quivering may lead to body spasms or verbalizations of the stressed individual's mindset. Extreme cases lead to a phenomenon known as rectal resonance (RR), manifestations of RR often include involuntary feces expulsion and can be highly amusing/unpleasant/pleasant for bystanders. QAS is a reckonisable condition and can be likened to, but is not the same as 'Shitting one's pants in fear".
"Before that test I totally had the worst QAS man".
"The whole date I had QAS, and when she began to blow me back at my place, I totally got RR and shat all over her".