First of all, I think your co-wprker overreacted. You did not say anything wrong to her. Why did she feel the need to report the incident to your boss? I was not raised in the area where I currently live. I purposely use slang and terms from where I came from just to get people's attention and be different. When people do not understand me they ask what I mean and we start a good conversation about language, etc.

On the other hand, you boss probaby had a bad day and did not want to get involved in a personal issue. If there had been a real problem she would have told you. You wanted to talk to her because you had anxiety about the situation and it is hard to just sit and wait when you feel so much stress. Your boss had no anxiety and didn't want to waste her time and energy on the issue. Next time just leave her alone and let her take the first step. Chances are you will never hear anything from her.