Shoving one's fist up a man's ass, and then opening up the hand up. Like a 'Mary Poppins,' but to a man instead of to a woman.
The two gay guys took turns giving each other chimney sweeps.
Shoving one's fist into a vagina and then opening the hand up, like an umbrella.
Bobby got his girlfriend, Sue, really drunk, and gave her a Mary Poppins.