breakin it down is when you just don't give a shit what other people think of you in your actions. Express yourself in the most personal sense of expression=!!
The insertion of one fist in a woman's vagina and the other fist in her anus, and then performing a dance move with the arms going back and forth in front of the chest.
chris: so what are you going to do to this chick tonight?
andy: im gonna pop my fists in her and break it down
chris: ahahahhahahahahahahahahahah
This phrase is used when you are about to explain something to someone in very basic terms because anything too complex will confuse them, or already has confused them. Frequently used in the military. Does not usually have anything to do with sex.