The term 'dirty side burns' originated in the porn industry, particularly films involving
ass-to-mouth (ATM) action. It describes the intentional act of leaving a shit 'lamb chop side burns' on a partner's face by the
dude taking his cock out of his partners
ass and slapping it back and forth across her face without wiping it off first. The result is that as the dick is slapped across her
cheeks, shit it comes to rest on his partners face in a 'lamb chop side burns" configuration.
After he fucked her in the
ass, he smacked his dick back and forth across her face,
giving her dirty lamb chop side
burns.