This phenomenon occurs when you drop a turd and the impact of the poo on the water sprays your butt-cheeks with a mocha coloured combination of dookie and toilet water. Most of the time collateral damage occurs when slaying diarrhea, since the glugy like substance enters the water at a fast rate thus creating alot of spray. Furthermore collateral damage occurs when taking a huge, but clean and fast individual log that enters the water in such a manner that it creates a fluctuation in water surface sending water particles to your ass. This is a weird sensation and is most effectively avoided by laying a thin layer of toilet paper in the toilet giving your beazley a smooth landing surface. Also this phenomenon can be avoided by dropping a grogan, which is a marvel if achieved since only the strong and the wise can do this.
"My ass is wetter than an indonesian swamp after that collateral damage"
"I just slopped the fattest diarrhea which caused monstrous collateral damage"
"Theres collateral damage all over the bathroom wall after i dropped that insane beazley!"