I've seen people wearing a tie with no jacket; they did not work at a cell phone store, nor did I think that they looked like they did. I've seen people wearing vests (with or without ties) without jackets; they were not waiters, nor did I think that they looked like they were.
I'm not sure if these alleged rules you speak of are codified somewhere, but given the context of the conversation (people around me are wearing hoodies and pajamas while I'm wearing a suit), I find it hard to imagine any combination of jackets, ties, and vests being truly inappropriate...
If you try something out, and think you look great, and find that others agree, then bin any given rule. But most people, most of the time, are most likely to look best following most rules.
Personally, I don't like the look or feel of a tie with no jacket, or a suit with no tie.
Exception: vest and tie with a stylish hat. Otherwise, yes, a suit is usually mandatory. I didn't expand on it for the sake of making my point. I'm glad some people on HN have fashion sense.
Yes, there is a tendency for it to look like service personnel, so you have to either make it look classier or more casual.
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