You Make Carrot Cake?
A rabbit visits a bakery and asks if they make carrot cake.
The baker says they don’t, so the rabbit buys a key lime pie.
This repeats several days until the baker is sick of it and decides to try making one.
The next time the rabbit enters, the baker proudly tells that they do have a carrot cake now.
The rabbit says: sorry, I’ll have to take my business somewhere else: I’m highly alergic and can’t risk cross-contamination.