Either a cancerous stick that one smokes (Cigarette)
Don't ask for a fag in the US, or tell anyone you're dying for a fag, or announce that you're sucking on a fag. This is suicide and despite your best efforts to convince the Rednecks otherwise, you will be forced to retreat to a hail of abuse, sticks, laughter or (if you meet dogface) flying lead hurled from a 12 gauge Remington.
To Fag (v): A junior student once used as an 'unpaid' servant by a senior student at the great universities in the UK. Although in today's world innocently asking someone to be your fag could result in your teeth going down your throat!