Notice who the jokes in your friend group are always aimed at. Laughing along is still choosing a side.

Most groups settle on a target, and whoever holds that position rarely got to volunteer. Laughter is the machinery that keeps it running, so joining in counts as taking part even if you never say anything cruel yourself. Neutrality is not really on offer in a room where everybody is laughing.

Count, over one week, whose name turns up at the end of the jokes. If it is the same person every time, try simply not laughing, which is quieter and more effective than a lecture. Then talk to them about something else entirely, as a person rather than a punchline.