Visit with an exit plan. Knowing you can leave makes it easier to stay kind.

Knowing you can leave changes how the whole visit feels, before you use the option at all. Most of the tension in a hard family gathering comes from feeling trapped in it, and that feeling is what makes people snappy well before anything actually happens. An exit you never take still does its job.

Arrange your own ride, pick a time, and tell somebody what it is. Then stay as long as it is going fine and go when you said. You will be warmer for two hours than you would have been for five.