In any other situation if someone disrespected me I'd tell them to fuck off.

But what do you do at work?

In the past I'd just play nice or be passive but is still think back to those customers like a year later and want to beat them senseless. I'm a very kind person and have strong morals and would never disrespect an employee or any stranger

The fact that people can actually do this without feeling shameful or remorseful makes my blood boil.

What should I do next time? Risk my job and go sicko mode on them?