Notice what someone laughs at. It tells you a lot about what they think of people.

Laughter comes out faster than opinions do, which is what makes it useful. Somebody can say all the right things about being kind and still laugh hardest when a stranger is humiliated, and the laugh is the more reliable report. It shows you who they quietly think of as beneath them.

Spend a week just noticing, without announcing that you are. Watch whether the joke is aimed at someone who is not in the room, and whether it needs somebody to be the loser. Then notice your own, because this is not only a test you give other people.