When you sneak off two have a ciggarete at fammily ocations
tod: Dad where is uncle jerald.
Dad: he snuck of four a crafty fag.
Uncle jerald: Thats good shit
When ones sneaks off to have a cigarette unnoticed. Used especially when one is not supposed to be smoking but does anyway.
John: "I'm just off out for a crafty fag round the back"