This is when the thickness of woman's thighs, coupled with her vaginal pelvic muscles, literally squeezes out the semen of a man's penetrated penis. Thus acting like a hand squeezing frosting out of a pastry bag.
"My girlfriends legs are so thick, and her pussy muscles are so strong, she literally squeezed the cum out of my cock! Like a Pastry Bag"
A manuever in which a tube sock (or any sock for that matter) is ejaculated into by a group of men and is then it's contents are squeezed out of the tip into a girl's or girls mouth/s.
The sock is meant to act as the "pastry bag," and it's contents the icing.
A pastry bag is like a bukkake, but with a sock.