A vegan shake is any form of sexual relations or acts with a female that is a vegan. Also interchangeable as a vegetarian shake, which is just with a vegetarian.
guy#1: Yo man that check is bangin'
guy#2: Yea man, i heard she is a vegan or something.
guy#3: I heard she makes good vegan shakes
When you have too much caffiene and not enough fats in your system so you get the shakes.
Damn shawty I can't sit still, I've got the vegan milk-shakes!