Yeah, I think it would probably be deemed to be a tip and not a gift. Just *saying* "this is a personal gift and not taxable" isn't a magic spell you can recite to make something nontaxable! Of course, nobody's going to actually care about an unreported, looks like $7 there, per se, but if it's a regular thing it could be a problem.

I think to make it stick you’d have to switch to a complete gift economy, where you regularly give gifts to people who aren’t currently providing you services, and don’t give gifts to people who are (as that is their gift to you).

That works for small groups, but doesn’t work so well in cities of millions where you can’t effectively maintain personal social ties with every single person you might possibly interact with. Then if you use an app or something to keep track of gifts you’ve just invented a new form of currency, which would actually be kind of cool.