I'm allergic to tomatoes and often ask to substitute them in salads or on the side of a dish when eating out for example to ask for extra cucumber in salad or a onion right with stake and chips. I got called out for being rude when asking to swap at the weekend by a friend - something I've always done and never thought was rude, just wanting to reevaluate if I need to change my requests and just accept my meal without the tomatoes.