Notice who laughs when you trip. Now you know who was waiting for it.

Reactions in the first second are the honest ones. A person who laughs before they check whether you are hurt has told you where they stood the whole time, and it is information you did not have to go looking for. Nobody has to be punished for it. But you do get to know it.

Keep the observation without turning it into a campaign. Adjust quietly: less shared with that person, more with whoever reached out a hand. And if a group makes a habit of this, that is not something you have to sit inside, and it is worth telling someone you trust.