1. When you drop a doogan in the toilet and it hits at such a force that water splashes up onto your cheeks and/or anus.
2. When you stand too close to a urinal whilst urinating and urine splashes back onto your shoes and/or legs.
"Shit, my arse crack is wet 'cause I got splashback from that toilet."
"Hey Joe, what's that all over your shoes?"
"Fuck don't you just hate splashback?"