Please Hold
Have you ever been on the receiving end of a phone call from a customer complaining to you about something your company did? It isn’t particularly enjoyable, nor is it helpful. But one thing it can do is provide entertainment for you and your coworkers.
If a customer is going to go all out at you complaining about something not even related to you, then yeah, you have the right to tell your coworkers about it. To be honest, if you didn’t have the ability to vent about your workplace then as a customer service worker you would actually go mad.