I have a scar on my thumb, acquired when I was 17.
For many years people used to ask me why I never touched spirits or anything stronger than draft beer. I would show them the scar and say "Thats why"
This would then lead on to the story of the time I was 17, and a big fan of neat vodka. One evening I managed to plough my way through 20 doubles to win a bet. At the end of it, I knew I'd done a very silly thing and attempted to make amends by drinking vast amounts of water. Sadly, while carrying three pint glasses from the bar, I dropped the lot. I bent down to collect the shards of glass, and managed to gash my hand.
Afterwards, its a bit fuzzy. I vaguely remember covering the bar's bathroom in blood, the worried barman saying "He *is* 18, isn't he?", being driven to A&E by a girl on whom I had a crush (not realising that my actions would have forever condemned me as a moron in her eyes. After all - getting drunk is big and clever... Isn't it?) and finally being threatened with a stomach pump by an angry nurse.
In the morning I awoke with almost no memory, a huge bandage and the words "Oops. Fucked up" on my lips.
It makes for a good morality tale on the evils of drink.
Unfortunately, that scar of 15 years ago is going to be eclipsed by the huge new one. And the story: "...and thats why I now only eat takeaway food. Washing dishes is dangerous" is not half as interesting.