If vegans can redefine "cheese" then why can't I redefine "vegan"? You're saying that only vegans can distort commonly used terms to promulgate their beliefs? T

If vegans can redefine "cheese" then why can't I redefine "vegan"? You're saying that only vegans can distort commonly used terms to promulgate their beliefs? They can sell "vegan" cheese as propaganda for their ideals but I can't just say, well then, you're not vegan because you're eating cheese? Why not?