A fork of Rural Dictionary
'assholes and elbows' refers to working hard at a task. It originated in farm work. If a group of field hands is busy and bent over picking crops, then a supervisor looking out over the group would see nothing but "assholes and elbows".
A derivative term with the same origin and meaning is head down, butt up.
Row boss to field hands: Alright that's enough chit-chat and coffee break! It's time to get back to work and I don't want to see nothing but assholes and elbows until this field is picked clean.