When you have a bowel movement without cleaning risidual fecal matter and then surprise a person by spreading ones "butt cheaks" and "smooshing" it against a person
Charlie gave Peter a brown butterfly while he was passed out from to much drinking.
It's the cousin of "tossin a salad". Instead of using your tongue to stimulate an anus, you use your eyelashes like a butterfly kiss. bananus
Sara was afraid if she blinked too much while the brown butterfly was in effect I would shit in her eye upon opening. I let her know I have control of my anus by letting a little fart out and taking a single eyelash with me as a keep sake forever.