Dirty Sewer Rat 

When you are inside a disgusting public washroom stall taking a dump and you get a chick to suck your dick during the process. When you are done pooping, she licks out your ass then you spin her around and stick your dick in her ass while shoving her head in the toilet that you have not flushed(this is crucial). After she has eaten approximately 50% of your shit start effing her in her pussy and slap her back with your right hand hopefully forcing her to puke up your shit. After this is accomplished take her out for an italian dinner and a movie.

Dan: Hey Dave I saw you and Kim out having dinner last night at Little Sicily, what was the occasion?
Dave: Oh nothing, we just did the dirty sewer rat earlier that evening.
Dan: No way! Did she eat enough of your shit?
Dave: No, but I let her get away with it.
Dan: That was nice of you dude.

Dirty Sewer Rat by dillonstott January 13, 2009

Dirty rat from a dirty sewer 

A person whom turns on you and screws you over for a girl, video games, or money. Any malicious act against you or your friends can qualify the perpetrator to be called a dirty rat from a dirty sewer.

Also can be called a 'filthy rat' or 'the filthiest rat' or 'the dirtiest rat from the dirtiest sewer' or just plain 'rat'

Guy 1- "That Chris is a dirty rat from a dirty sewer."
Guy 2- "Yeah, the filthiest rat from the dirtiest sewer."
Guy 3- "What a dirty rat!"

Dirty rat from a dirty sewer by Rat Keeper March 23, 2011