Sorry for any typos, I'm on my phone.
I work one or two days a week as a volunteer in a tiny charity shop in our small town. It's usually pretty quiet. The shop is open until mid-afternoon.
Today I was having my sandwich at the register, the shop had two or three people browsing. One came up to me just as I'd taken a bite, and I smiled behind my hand, swallowed as fast as I could, then greeted her with a jokey "sorry about that, can I help you?" At which she tutted at me, frowned at my sandwich, and said "you shouldn't be doing that, when you've got customers."
Problem is, I'm the only person here. I either eat at the register when the shop is quiet, or go the day without food.
Would you be offended by this if you were the customer? She's the first to ever comment about it.