Dresscode

What was first class travel dresscode when it applied, like 1950-s, 1960-s?

Was it enforced – i. e. were people with paid tickets liable to be denied boarding or involuntarily downgraded for failure to meet dresscode?

When did the men only flights operate (so that men could remove their jackets – since stewardesses are no ladies)?

When did dresscode on commercial flights disappear? (In which countries?)