Depends on what kind of food we’re talking about. Are we talking about a sandwich someone took a bite out of, or say, a half a plate of french fries or whatever?
I’m not going to take something a complete stranger bit into (hey, want this sandwich?), or whatever, but my friends or family? If it’s something I like and I’m hungry? Meh. You’ve NEVER shared food with a friend? Popcorn? A plate of fries?
One time a co-worker and I got Chinese takeout, then she went on break before me. When I went to go eat my shrimp and broccoli, it had chicken in it. She said, “I couldn’t finish my chicken and broccoli, so I gave you the rest.” She had just scraped her leftovers into my takeout box.
So, there’s one person out there who has no issues with sharing food. I’ve learned that I can give her my leftovers, and she’ll eat them, sometimes a week later. I’ve also learned not to leave my food out around her.
Nah, I’m not too picky. I figure most people I’m in close enough contact to eat their food I’ve already shared most of their germs one way or another, and survived.
Today I was eating my lunch and a coworker was commenting on how yummy my leftovers smelled, I offered him a forkful of mashed potatoes with gravy. He ate it, I went right back to eating and neither of us thought anything about it until we got a raised brow from a third guy at the table. Meh, I’ve got an immune system and it works.
3 seconds processing this… and I spit coffee on my monitor. Score, Contrapuntual.
Well now I definitely don’t want that coffee.
A friend of mine and I often eat lunch together at work. We swap leftovers. Sometimes only one of us has something to share. One plate, two forks…not a big deal to either one of us. We drink out of the same pop can, too. That should answer your question. Eating after someone is OK by me, and him. He’s a good friend. 
Like others in the thread, I’d finish the leftovers of family and friends (moreso the former), but definitely NOT of strangers.
I wouldn’t. But I don’t even eat my own leftovers.
Family & friends, no problems at all. I’ll even use their fork/spoon if I have to. Is there really a risk of disease transmission from spoon sharing?
As for acquaintances, probably not. And not because of cooties, but food sharing imparts an air of closeness that I don’t really want to impart to mere acquaintances. It’s like the intimacy “signal” that Elaine (of Seinfeld) got from an acquaintance in the gym when he offered to let her take a drink from his water bottle.
If it’s a friend or family, doesn’t have gross eating habits and I’m hungry, yes. If it’s a stranger, no. I’ll also accept food from acquaintances (such as that people from work you only meet at the coffee machine) if it’s something that’s prepared to be shareable, such as cookies or fruit that hasn’t been bitten into (“I brought two oranges but only got room for one, anybody want the other one?” was a common scenario at my last job).
The “yes” was much more applicable when I was a teenager, back then I would have eaten almost anything all of the time.
I come from a culture where people dip their utensils into a common bowl or dish in the middle of the table . . . so no, I wouldn’t have a huge problem with it, unless they were obviously sick or something. Or if it were something like soup or yogurt (unless it’s my boyfriend or a family member).
I just remembered that I’ve shared joints before so that makes this hangup a bit weird.