a dirty berty occurs when your partner is giving you oral sex under a blanket and you fart and hold them under the blanket to continue while they smell your fecal odor.
after having anal sex, the man pulls out his penis and wipes it across his partners eyebrows, forming an a thicker eyebrow similar to the Sesame Street Characters.
The purpose of a dirty Burt is to make a passed out friend look like famous actor Burt Reynolds. The way one does this is by taking a steamer and letting it cool. Then get a glove or if your real brave pick up the POOP bare hand and and place it on your friendsupper lip. Thus making it look like he or she has a Burt Reynolds mustache.