I strongly dislike ketchup, but my sister is addicted to it. If people think you're weird for dipping a sandwich into ketchup, let me tell you... my sister used to mix ketchup into her mac & cheese, into her tacos, and on corn. I would say that sandwich with ketchup is nowhere near as bad as that.

Edit: she also used to pour ketchup onto salads. I think that is beyond gross, but whatever floats her boat