Interesting issue. I tend to: 1) Take a lot of shots, also when people are sober. Take a lot of photos and the folks might get used to you running around shooting the whole time. 2) Make jokes or being silly. This makes the atmossphere less causal, less "do I look good like this?" and your subjects may be more relaxed. 3) Use the SB-24 "red light" to play around with, often using it to be able to pin-point what I am focusing at when I have the camera at my belly, triggering. 4) Use the 80-200/2.8 to be able to get close w/o people really getting it.
One of the shots taken at living systems' xmas party 2000. Nikon F5, Nikkor AF 80-200/2.8 and SB-24 at some 100mm on Provia II
And other one of our Brazilian software engineers at the same party. Same gear and same type of film.