Hybrid of "Cho" Seung-Hui (the Virginia Tech gunman) and the term "going postal", meaning to suddenly become extremely and uncontrollably angry, usually to the point of violence. Going "Chostal" is exclusive to violent or homicidal incidences at schools or institutions of learning (libraries, etc) and more than not culminates with the aggressor killing him or herself.
William was so tired of being picked on throughout high school that he went straight Chostal at the prom and shot twelve people then himself.
by Eric T. James May 23, 2007