A great comeback when someone insults you. On a scientific level this works because the things we eat actually make up our bodies. But if you were called... for example... a pussy... you get the idea.
"You never do anything daring. You're such a pussy"
A saying that is used when someone who eats pussy acts like what he eats. (substituting the noun pussy for the verb pussy).
Gangsta 1: You fronted that nigga 2 pounds because he was rolling deep.
Gangsta 2: It aint even like that.
Gangsta 3: You are what you eat. (as he cocks the desert eagle).