Similar in process to a Dirty sanchez. There are 2 times this can be done:
1) When a man, after anal sex, puts his finger inside a girl (or guy's) ass and takes alot of shit on his finger and wipes the crap above the his partner's lip, which resembles a hitler-like moustache.
2) A sleepover prank. When someone is sleeping wipe shit on above their lip.
The only diffrence between a shitler and a dirty sanchez is that a shitler is thicker and has more crap then a dirty sanchez.
1) Yo you gave that guy at the sleepover a shitler?
2) Yeah but i didnt bang him up the ass!!
After having butt sex with a dirty ass, you pull your shit covered dick out and smear a little patch of shit on the fuckee's nose. Then you pull out some of the fuckee's pubes and you sprinkle them on the smeared shit. Then you stand up and salute while shouting "Heil Shiter!"