I just don't follow a diet "strictly at all times". If you're (truly) following your diet 95% of the time and go out every-other Friday (or hell, even if it is every Friday) for a social dinner, 1 meal of 21 or 42 meals isn't going to completely ruin your dieting any more than forgetting to brush and floss after lunch on Thursdays is going to completely ruin your teeth.
If you go out for social dinners every single day it might be a problem - but that is pretty atypical.
I feel most people could benefit from "following a strict diet 95% of the time" over "not dieting at all because I like pizza during my weekly Saturday D&D nights".