Let's say it's for something petty-ish. Like they grabbed the last mango at the supermarket that you had your eye on and were walking over to get it. Idk you're the witch so you can choose your level of vindictiveness. Explain what they did if it's fitting in with the curse.
All things meat or plant oriented in their kitchen will rot twice as fast as it should, leaving them with nothing but shitty hyper-processed foods that will predispose them further and further to joint inflammation and acid reflux. I don't wanna kill 'em, I want to inconvenience and enmire them in small, if chronic petty pains, and overall misery.
remind me not to fuck w/ you lol