milstil:

All true Sinatra fans must know the Ten Rat Pack Style Rules:

1. Never wear brown after dark.
2. Jack Daniels. Always Jack Daniels.
3. Give the ice a few minutes to sink into your glass.
4. Hats are to be tilted. Unworn coats are to be carried nonchalantly over one shoulder. (Frank got this from Jimmy Van Heusen)
5. Sinatra’s orange fuzzy sweater at the beginning of “Ocean’s Eleven” was an anomaly.
6. For the ultimate sign of friendship, share one of your martini olives.
7. Cuff links.
8. And a tuxedo.
9. But never on Sunday.
10. The worst thing you can do in front of a woman is yawn.

Bill Zehme, “The Way You Wear Your Hat” (HarperCollins, 1997) 

David Niven, Steve McQueen and Miles Davis follow the rules.