Depends - are you keeping the diet a scret or are you afriad they will think its too hardcore? What exacty are your concerns?
I hae found every one supportive, so not encountered any Spanish Inquisitions.
Its difficult if its because you are akkeping it secret, which I did until it became obvious. I just told people I had already eaten, or I had a funy tumm, or had a root canal and mouth too sore so I am on a liquid diet for the interim, etc.
If its because you expect them to be too nosey - be firm, but polite, and tell them you are choosing to deal with some health issues, and this is under that care of your doctor, etc., etc., If they push, or get negative, become firmer. This is YOUR life - and you have the fina say.
These events usually go better then planne, and the reaction from others is usually bettter then expected too.
As for holidays - its perfectly acheivable to abstain 100%. This past spring I wnt back home to California for moms 90th birthday. Lots of parties - lots of events - a couple road trips, 3 BBQs, and life in hotels and airplanes, hubbgy eating in roadside retaurants, etc., etc., and I managed to stay 100% dedicated....it took some effort on my part, but the point of it is I was on a diet. Holiday is not a "get out of diet Free" card....so if you want to bad enough - you find ways t make it work.
There is no situation this diet cannot work in.
Good luck!