I've watched a woman walk into a space to meet her group -- all of whom were women -- and address the group with "Hey you guys!"

I've also worked with a woman who was extremely displeased to be greeted with "you guys". I found her absolutely insufferable.

The reason it feels bad to people who use "you guys" in a gender neutral way is what it says about the offended person. The offended person has a pet peeve, and if you don't accommodate it, it will be a problem. That's pretty much the definition of an insufferable person.

A person who is well-regulated wouldn't make a stink over something so trivial. Which then tells you that the person is going to make a similar stink over other trivial things. Ad infinitum.