When one person says something to offend another. Also you can say just burn, but burn down the side is reffering to side burns, like the facial hair. And when this is said instead of just burn it makes it more offending.
Rochelle: Well at least I don't eat 20 meals a day!
Kaytee: Well at least I don't throw up the meals I do eat!
Bria: OOO BUUUURRRNN, DOWN THE SIDE!