Do you have any idea how much I love it when someone I know (ie. an acquaintance or higher) eats off of my plate without asking? DO YOU KNOW? I understand why some people might be aggravated by such an act since it might be considered rude - but I love, love, love it. It's so bold and almost, like, a friendly kind of bold. I really think that we, as a society, need to stop viewing this act in such a negative light. Why? Here are some reasons.

Sharing is caring. We learned that a long time ago, let's bring that phrase back.
When someone is too hungry to ask for a bite, it's a lot faster to just take it - we've all been at that level of hunger before.
It's so loving! I might have germs, but does this food-snatcher care? Nope! Not a care in the world! If I've got a cold, well, now you've got a cold, bud. Doesn't bother me, we're friends!
Offering someone a taste of your meal with the hope that the person you're with will offer you some of their dish is almost MEDIEVAL at this point. JUST GRAB IT AND EAT IT.
If I've made a bad decision when ordering my meal, I need a backup. Your meal is my backup. Get on board with this. If you find that to be selfish, please keep in mind that this is a two-way street.

Do you need more reasons that that? Seriously, I will email you more reasons if you ask me.

In any case, if you and I are ever in a restaurant together - be prepared to have your food eaten by me. It's 'cause I love you.