When you have a powerful poop, that spashes copious amounts of toilet water on you butt.
I used the portapotty at the fair and the poop caused some cirque du soilet
When a poop exits the anus and then re-enters because of a loud noise or an unexpected scare.
Last night I was pooping during the thunderstorm and lightning hit the tree outside the bathroom, needless to say I had a peak-a-poop.