A group or party almost completely composed of men. A beef fiesta has more men present than a sausage fest. Those unfortunate men who end up at a beef fiesta end up feeling violated and go into shock after exposure to the unholy and massive amounts of wiener present at a beef fiesta.
Alex - Dude, I almost went to that shady party down in the valley. I heard it was a total beef fiesta!
John - Man, I bet you're glad you didn't go.
Alex - Hell yeah.