وَإِذَا مَرُّوا۟ بِهِمْ يَتَغَامَزُونَ
Wa izaa marroo bihim yataghaamazoon
and when they passed by them, they would trade mocking glances,
The Arabic verb is reciprocal in form, so the gesture passes between the mockers more than it reaches the person mocked. That is how the whole passage tracks it: laughing among themselves, signalling as they walk past, then repeating the joke once they are home. Sura al-Mutaffifin opened by weighing short measure in the marketplace, and this is the same short measure given to people.