I have only very recently been diagnosed (Type II), so I certainly can't claim to be an expert on this. However, I had to face this issue immediately - quite literally the day after I got the news I was planning to go to a friends stag party - and even if one accepts modest drinking, getting hammered on a stag night is probably not a good idea.
I was tempted to either to put off the diet for a day or drop out of the party. However, ignoring the diet and drinking as normal would be really bad psychology (the problem with putting things off until tomorrow is that tomorrow never comes!) and as for not going... well, I must control this thing, I am determined that it will not control me. I also really didn't want to make a big announcement to my friends - not that I intend to be secretive about it, but the timing could have cast a real pall on the event and that would have been unfair to everyone. So, the only solution that I could think of was compromise. I started off by turning up late (it was a pub crawl from lunchtime to midnight) - I pleaded overwork and turned up at about 6pm. Then I had a pint when we arrived at each pub and thereafter mostly stuck to mineral water, interspersed with the odd half. I ended up drinking about four pints in the evening. Probably not ideal, but vastly less than what I would have drunk otherwise. Now all I have to do is figure out how to get through the wedding :?