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1.
1. When somebody destroys the bathroom with shit.
2. When somebody's taking a shit while having a spasm
Man I went to the gas-station bathroom, somebody took a shitsizm, the toilet wasn't enough to contain it, it was smeared all over the walls.
by metallica36 April 03, 2013
 
2.
defecating uncontrollably, usually in a public bathroom of a less then fine establishment, i.e. truck stops, gas stations, waffle houses, and leaving the mess for others to have to witness
Man, some loser shitsizmed all over the bathroom stalls!!
by bernieburned1 April 04, 2013