It's no fun being left out. It's no fun being excluded—from a club or a party or just a conversation. A friend of mine says one of his most vivid childhood memories is of being left out—in a car full of kids, while his aunt went shopping by herself. Forty years later, he still gets a little burned up when he thinks about it!
Apparently a lot of people feel the way my friend does. Maybe that's why there's so much talk these days about being "inclusive" in the way people speak and act toward each other. The idea behind inclusive language, for instance, is never to leave anyone out, for any reason—not because of race or nationality or age or sex or religion or economic bracket, or any other human classification.
Sometimes, though, it's hard to remember to be inclusive. If you and I were both plumbers, let's say (or computer programmers or Bible scholars), we might get so absorbed in talking to each other in our own language that, when we're with other people, we forget all about speaking in language that includes everybody—language that everybody can understand. We might get so absorbed in talking about "widgets" and "pipe fittings" and "seepage pits" that we forget that some people have no idea what these terms mean. So, without really intending to, we speak in exclusive language. In language that can make other people feel left out.