I'm going to eat raw onion because my boyfriend really dislikes the smell.
Why are you trying to gross him out?
I just want to see what he looks like while having sex after I do it.
There's nothing wrong with eating a food you find yummy, but you know your boyfriend hates the smell and will be bothered by it. You shouldn't annoy someone for your own amusement, especially a romantic partner. It will just make them angry at you and will make them rethink if they want to be with you or not.
Why? Girls love the smell.
He does not though. I think that it is mean to do something that you know is going to upset your boyfriend.