How would you define the term "Gentelman's Habit"?

I was trying to define it to someone I know but I couldn't think of a way to do so. For example at night I will read or watch a bit of TV at night while sipping on some Scotch or Whiskey. Likewise a buddy of mine will have a cigarette at some point in the evening before bed. These are (from my understanding) a gentleman's habit. But how would you define the phrase?