When you jack off into your mouth in order to get your protein for the day.
Yo Jordan I had the best protein shake ever this morning!
When six men cum in a girl's vag, hold her upside down, shake her, and then pour the contents into a cup and she drinks it.
Back in my day, when I craved a protein shake, I'd pop over to Belind's house with my five mates and have an australian protein shake.