Getting catcalled is a staple of many women's existence, unfortunately. Women oftentimes feel unsafe and scared when they are alone because many men do not respect their space or boundaries at all.
When women are alone, or even when women are together in groups, men feel that it's okay to yell, whistle, or hoot at them from a distance in order to express interest. Women are sick and tired of being seen and treated like objects. So some of them explained on Reddit what they do to counter catcalls.