Sudden Onset Defecation

Sudden Onset Defecation or S.O.d. which is difference between let’s stop at the next rest stop and PleasePullOverNow!

“Damn Ron, what took you so long?”
“Well Dave, I had an emergency Sudden Onset Defecation and barely made it to a WaWa.”
“Oh I understand that. I had a SOD last week and I’m not allowed in Walmart anymore.”