You don’t owe a reaction to everyone who’s performing for one.

Some behaviour is aimed at an audience rather than at you. The loud comment in the corridor, the post that is obviously about somebody, the provocation staged in front of friends. Reacting completes the performance and makes you part of it, which was the point. Walking past is not a failure to notice, it is declining to be cast.

Decide in advance what your face does when this happens, because deciding in the moment is hard. A nod, a neutral look, carrying on with what you were doing. Save your real responses for people genuinely talking to you.