I'm going to serve a customer exactly what he asked for even though he said he was also allergic
I hope you are joking. Is this something you do often?
Yes. It happens from time to time although I'm usually sure when a customer is lying about his food allergy.
It is wrong to serve someone allergens if they ask you not to. You could kill someone if they are not lying and should respect their wishes.
I have no sympathy for people who have an allergy, they should have been more responsible and not ordered the food they are allergic too.
People should be able to order what they want when they go to a restaurant. It is easy for a chef to take out what the person is allergic to before serving the dish. If you know they are allergic you shouldn't give it to them on purpose.