This term is used when two or more dudes, either gay or seriously plastered, both take a shit on the floor, mix it up, then see who can bust a nut on top of it first. The last person to jizz has to eat the steaming pile of dung topped with snake juice!
Gunther and Shane were so drunk and bored at the party, they went out back and made a brownie sundae. We knew because Gunther's lips were covered with shit and cum.
When a guy takes a crap in another guys mouth and then the guy with the crap in his mouth sucks the other guys dick... so then the guy that crapped had his own crap all over his dick and then he gives the other guy anal, transferring his crap in to the other guys anus.
"Hey, your crap is in my rectum because of that brownie sundae"
"A brownie sundae is the dirtiest thing you could possibly do."