You've brought up a good point. Where's the line? This is something I ask myself and the people around me every day. The thing is, it's not black and white. It can be extremely subjective to each person's feelings. How do we know when someone is in need of standing up for etc.
In your example of Chris, here's how I see it. Saying you have a crush on someone is harmless. Chris has not reached out to that person, explicitly hit on them, and been disgusting about that persons body. Sure, maybe she could see the word "crush" and depending on her own experiences and feelings, may feel threatened by that. Personally though, I think my line is drawn when things are taken to a sexual manner.
Someone could walk up to me and tell me I am beautiful. I say thank you and carry on. This would not bother me. It's the second the person turns my body into an object and it turns sexual that suddenly I feel a little uncomfortable.
I think setting is important as well. Work vs real life. Work can be a tricky place to navigate because talking about a person's physical appearance is a thin line to walk. Typically in a work setting it's most safe to just talk about work or performance and never the physical appearance. It's unfortunate because we want to connect with the people we see every day.
I think in all of this, my point is that it's tough. It's hard to know where the line is because the line for everyone is different. That is why consent is SO IMPORTANT. "I think you are beautiful, is that okay to say?" It doesn't hurt to ask permission. The mere asking of permission shows the other person you respect them and their feelings. It's easy to do and doesn't take more than an extra 5 words to check in.
Or on the outside, if you see an interaction and you see someone looking uncomfortable, check in on them. "Hey are you good?" You'll know, even without them saying it if they need help.