1. When your father-in-law is moaning about the price of gas at $2.29 a gallon and his little yellow light on the dashboard is on, don't say "isn't $2.29 cheaper than a tow truck?"
2. In the middle of dinner when your father-in-law continues to fill up your husband's glass with red wine, don't say "you probably should stop doing that because you might need a part of his liver some day."
3. Do not follow your in-laws into their hotel room 2 minutes behind them without knocking on the door, even if they know you are coming. You may find your father-in-law climbing into his bed. If you do, do not (and I cannot stress this enough) shriek loudly and go running from the room. We're all adults, for heaven's sake.
4. Do not cover your ears and start humming when the discussion goes south and suddenly you are in mixed company with your mother-in-law discussing the conceiving of your husband. There is no song loud enough to drown out the phrase, "and I was so horny I borrowed money and took a train across country to meet Derek's father." I know they did it at least once, and I am VERY glad for them, but I really don't need to hear about it.