If you could go back in time and change one thing, what would it be?

I'd have joined the navy at 18.
Worked until i was 45 (assuming i'd have survived the Falklands and several trips to the Middle-East since '81)
Retired on half-pay and be kicking it in the Caribbean today.

I think that incident 2 years ago that haunted me a long time and still haunts me time to time.

I'd go back to when i was like sixteen I'd pick one day when the lottery was astronomically huge and make myself the winner!