[mothered]

Given this Is relative to SEing, I've moved It from The Lounge forum to Social Engineering.

In answer to your question, food Is the easiest commodity to SE. Simply saying you felt sick "Immediately" after consumption, works (almost) every time.

What restaurants can I apply this to? Does it have to be a in-person thing or can it be done over online?

It can be done In-store, over the phone or online.

Companies/restaurants take health and safety seriously and have a reputation to uphold, hence the reason the SE works almost every time.