This is an idiom that generally means “in the presence of people who might be offended by something.”
There’s no precise definition, but the “mixed” refers to a mix of people whom you intend to hear something, and those whom you do not intend to hear something.
Breaking it down a little further, “company” is used in the form of “a group of persons; one’s companions or associates; a guest or guests.” In this form, company means the group of people who would be exposed to the information.
You often hear this in the form of, “I wouldn’t tell that joke in mixed company.”
- A sexist comment in the presence of a mix of males and females
- A racist comment in the presence of a mix of different races (or, more specifically, members of the race who would consider the comment derogatory)
Why I Looked It Up
I just got to wondering one day if there was some fixed definition for this (there is not).