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.
Really bad diarrhea every time they eat their favorite food
Wait, were you the robed figure who I cut in front of at the pub that fateful night four years ago.
If by robe you mean bathrobe and by pub you mean my kitchen, then yes