Teasing only works when both people are laughing. If one isn’t, it’s just mean with a smile on.

Teasing runs on an agreement that both people are in on it. The moment one of them stops enjoying it the agreement is over, and what continues is not the same activity, even though from outside it looks identical. The smile on it is what makes it hard to object to, which is part of why it keeps going.

Watch the face of whoever you are teasing rather than the people laughing around you. If the laugh has gone thin, stop and say you took it too far. And if yours stopped being funny a while ago, you are allowed to say so.