If someone opens up to you and shares a story or vents about a time they were mistreated or disrespected, now is the time to listen and show compassion. It's not the time to one-up or flex about how you think you would have handled the situation. It's also not the time to lecture them on how you think they should have responded, or to shame them if you don't think their reaction was adequate or assertive enough.
For example, your friend opens up to you about the time he tried to have a nice dinner out with his partner, but restaurant staff were being racist/xenophobic and refusing to seat them, so he and his partner just left and found somewhere else to eat. Now is not the time to flex "Well if that were ME I wouldn't have just taken it and left, I would have totally put the staff in their place and not tolerated that!"
Or, for example your co-workers tells you about how she went to the grocery store last night and right as she was about to check out someone aggressively cut her in line, now is not the time to shame her / put her down with a response like "What, and you just took that? Oh come on you can't be such a pushover!"
First of all, you don't actually know how you would have responded in these situations. You don't know if you would have actually frozen or fawned in these situations. Many people do, even if they don't think they would. And that's okay. People don't just decide to freeze or fawn, it's an automatic reaction. Stopping behaviors like freezing or fawning can take years of therapy, not just a belittling lecture from a friend or co-worker.
Or even if someone didn't freeze or fawn, they just made the conscious choice to avoid a confrontation. That's also okay, and not your place to shame them. People can have all sorts of reasons for wanting to avoid a confrontation, such as not feeling it's safe, or feeling like it will just make the situation worse.
Second of all, responses like this can come across as belittling and generally insensitive. Even if you don't mean it that way, it can come across as though you're trying to insinuate that you think the other person is lesser than you for not reacting how you think you would have reacted. When someone has already dealt with being mistreated the last thing they need to is be lectured or put down, it's rubbing salt in the wound to respond insensitively when someone opens up to you about dealing with mistreatment.
Instead, show compassion. Tell them they didn't deserve to be treated that way, and what the other person did was wrong. If they're being mistreated by a boss or co-worker, kindly remind them that they have the right to report the behavior. Or if they're being mistreated by a classmate or teacher, kindly remind them that they can speak to someone at the school about it.
You can kindly remind them that in the future they're allowed to stand up for themselves in these situations, if they choose to, but don't lecture them or shame them for not responding how you think they should have.