Okay, I wanna say that you're right. It's never an okay and cool thing to say to an employee that is working for you. However, let me give you some of my perspective, because I can easily see how stuff like this can happen by accident or "innocently".

I'm socially retarded, I might even have a tad bit of autism. Social ques for me are just hard and sometimes takes a while for me to figure out. It's like a science at times.

So I think "Calm your tits" is an expression used for basically "Calm down", "Don't get too excited" or "Take it easy". And I can easily see two close friends taking this expression a step further and adding "Calm your tits and twerk for me!" as a fun way to say "Don't get too exited but get exited"

Now I could easily see a younger me stumbling upon two dudes having this social interaction and hearing this new fun expression and wanting to try it out myself without thinking of how or to who I'm saying it to. So yeah, I could see shit like this happen by accident and without malicious intent.

I'm a grown up. I realize that the things I say and how I say it have consequences. The things I say to my friends might not always translate well into a work environment social setting.

So could this happen? Yes (at least I think so)
Should this happen? No.

If you're a businessowner you have (for lack of a better word) "power" over your employees and you can't go around using expressions like these in a professional setting.

Sorry for the long reply, I agree with you, just wanted to add some perspective! Have a good day! <3