When after engaging a girl in anal sex, she proceeds to spray diarrhea all over you. It is actually a mix of semen and feces which has an odor similar to very old muffler grease.
I was butt-fucking Pamela after she ate 3 steak soft tacos. Right when I thought things were cool, she blew her dirty muffler all over my cheast. I'll never eat mexican food before sex again.
by EJL Supreme May 07, 2006
When a hot chick sits on your face and farts; drowns out moans and/or screams.
I was 69'ing with Kim when she sat up and gave me a "Dirty Muffler".
by Big L 11968 June 01, 2011