An exclamation utilized when you're angry, upset, annoyed or simply feeling random. It is frequently abbreviated as "BOMF!". The shorter variant, "Balls!" is also used, and can also double as a noun (synonymous to bullshit or crap).
Tom walked into the room and suddenly yelled,"Balls on my FACE!"
Leslie giggled and said, "What happened this time?"
Tom waved the paper in his hand. "I totally just failed my Orgo exam!"
Bella gets bumped by a stranger while trying to light her cigarette and it falls to the ground. "Oh, balls! That was my last cig."
Facebook Status: BOMF! I can't find my keys.
Frank pointed ahead of him. "Dude, look at that huge line for the bathroom."
Greg stared incredulously at the line. "Oh man, this shit is balls!"
Frank nodded in agreement. "Straight up balls."