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...