If someone shows any interest whatsoever in what I'm about to eat I offer them a sample, even if I've never met them before. If they take a portion I'm much happier about accepting a taste of theirs.

I prefer this to happen as quickly as possible after being served so that any germs from people's cutlery are not included (I'll never use anything that's been in my mouth to aportion portions).

With my husband and immediate family, 'mi plato es tu plato'. My husband does take much more stuff from my plate than I do from his. The only things I can't stand sharing are especially prized morsels that I might have saved until last (so that I can fully savour them). Bugs me no end when these get filched from under my nose - thankfully not too often!