If I have any caffeine in the next year I will donate £100 to the Conservative Party.

Rules: tea in someone else’s house or a social outing is fine (I’m already awkward enough to cater for and it’s negligible amounts of caf). It’s also fine to have caffeine if it would make me safer to drive as per normal safety advice. Caffeine particularly and very definitely includes dark chocolate.

EDIT (one year later): I certainly made full use of ‘when it would make me safer to drive’ for any long car trips. The hardest part was the end of the first week. I didn’t think I consumed much that much caffeine (I thought I used it badly on an occasional basis) but it I was extremely uncomfortable with constipation for from about the 5th to the 9th day. The commitment above kept me going through that period. Once over that problem, it was fairly well integrated into my life and the main worry for the later nine months was that I would simply forget and I would be halfway through a Cola-cola on a rare evening out before remembering.

I am much better without caffeine and indeed, those times I have some to make sure that I’m alert when driving I find I suffer for days afterwards.