Saw RulesofThumb.org on Let wonder replace worry by the goal of the site is to collect every rule of thumb together in one place. Many of them are amusing and hole at least some truth – great for random interludes in talks.
Two of my favourites so far:
When starting a game of ‘rock paper scissors’ always start with paper – as a rule of thumb, most opponents will start with a rock as it’s the shape a hand most easily forms.
If a rich person you want to impress is treating you to a fancy restaurant meal and you don’t understand the fancy menu: order the second most expensive dish. It will be good and your host will be impressed with your decisiveness.