it means getting singled out of the safe picks. originally based on pulling one string from many that hold in a palm where one of them is shorter or colored red in the other end hidden inside the palm
in some countries this is done by using chopsticks in a container that one of them is colored in the end to pick someone from many by pulling the sticks at the same time for everyone
It seems that I won't be going anywhere this week since I don't pick the short straw this time
when your "doing" a chick {or guy in some cases} from behind then pull out spit on her or his back to make them think you cummed then when they turn around punch them in the nose and cum in there face
While face fucking your drunken slutgirlfriend, you pull your wang out of her mouth, cum directly in her face, and proceed to punch her in the nose, thus giving the effect of a strawberry short cake.