What cirumstance are we talking about here? Is this food at a function of some sort, or at school or a workplace? Was there a sign or some indication that the food belonged to someone else? If not my reaction is to finish eating and tell said individual to get cancer and take a long walk off a short pier (add profanity or other ailments to taste).
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The only saving grace of the present is that it's too damned stupid to question the past very closely.
H.P. Lovecraft
"Pickman's Model"