Don't talk about people unless you are talking to that person. To do otherwise does absolutely nothing constructive. It makes people feel outed and ganged up on, and can do wonders for cementing your own views on people, either based on the efforts of others to make you feel that way about them or based on your own baises.
"Hey, did you hear about Susan? She heard back on her biopsy today, and it's positive. She's going to let the team know later, but I wanted to give you a heads' up because I know you're working with her today and she may be a little scattered. She could really use our support right now - she's got a lot going on." "I'm worried something's going on with my friend. She's stopped eating much and never comes out any more. Last time I went to her dorm, there was trash everywhere and even old food in her bed. She just seems trapped. I don't know how to talk to her about any of this, though. Do you have any ideas on what I could do?" "Drew's a great lawyer, but he tends to go off on tangents unless you really pin down the direction of the conversation. I noticed your meeting with him yesterday got off-track. Maybe it would help if you could really drill down to the specific legal language that applies to the situation you're trying to get his guidance on next time." "Hey, Mom's in a bad mood. Might be a good idea to lay low and stay quiet for a couple of hours. She said she was going to take a nap, but she looked a little teary-eyed. Heads' up, sister/brother." "I love our head of the department, but she's going to judge you if you come into work with green hair or visible tattoos." Tell me what's not constructive about any of the above. Don't be so pedantic. There are absolutely tons of scenarios where it's appropriate, even considerate, to talk about people to others. People are social creatures who do not live in a vacuum. We talk about each other. Sometimes, it's helpful to have our friends talk about us to others for us - when a significant trauma is experienced and you're too exhausted to tell people over and over again, you can sometimes depend on mutual friends or a key coworker to help clue everyone else in that you're dealing with something which is hard for you to speak about. Sometimes, others talking about us can actually help lesson our own burdens. I love black and white, but this ain't the line you wanna draw and die on, pardner.
There's this wonderful quality we all have, that you are pretending to lack. Common sense. Use it. A bunch of petty exceptions say nothing about the point I was making.