When you shit on your partner's chest and then your partner comes to spoon with you and rubs it against your back.
Dan had some bad sushi last night and accidently shit on his wife's chest while making love, so she cuddled up with him and gave him a spoonful of brown sugar.
circa 2002 - When a black man and woman have been friends since their childhood or a long period of time, and have built up an attraction to each other but hides it, before it finally comes out.
"Brian and Christina are brown sugar - I don't know why they frontin'."