I can't recall my first one, it would have been either in a pub when I was 16 or the home-brew I made during the same year.
About a year before that I'd discovered a beer-off that sold alcohol to minors, so I got myself a flagon of cider and drank the lot, just to find out what all the fuss was about. It just made me feel a bit woozy. Took me another year or two to realise there was a social dimension to alcohol......I'd stayed on my own for the cider experiment, but I later worked out that the idea was to get smashed with friends and then brag about it. So I did a bit of that (luckily the friends were reasonably nice kids), but after a few sessions I just got bored with it.
I do recall the first drop of alcohol that I ever drank - it was literally a drop, when I was about 8 years old. My parents had had a small party and I found an "empty" with a drop still in it. I didn't like the taste, and I felt rather ashamed of myself afterwards, as if I'd lost my virginity or something. In those days temperance was still revered by some, and I'd heard somebody praised for having never taken a drop of alcohol in their life, so I thought "that's blown that one."
I'm a bad man.