So first off, before I begin, I'd like to clarify what these terms mean, since I realize not everyone might be familiar with them. The word neurodivergent refers to people who have mental disorders of some sort (that could include both illnesses and disabilities). The word neurotypical refers to people who do not.
Oh, so you're a psych major? Oh, you went to a group therapy class led by your high school guidance counselor? Cool! That's great! But don't think that means you actually know shit about mental health if you don't struggle with it. Don't think that means you get to tell a neurodivergent person that they're wrong about something pertaining to their mental health, just because you happen to have studied and researched what they're going through-- when they're the ones who have actually gone through it.
Don't get me wrong, it is perfectly okay to offer words of advice and support to a loved one experiencing a mental disorder of some sort, especially if you may know good suggestions for them based on what you have learned in your studies. But there's a difference between genuinely loving advice and condescendingly telling someone what they need or don't need to do to benefit their mental health when they already know.
Like telling people they do not need medications for mental illnesses, or that going outside and getting "fresh air" or whatever is a better cure for them. Okay, so who the fuck made you the expert on how to best treat someone's mental health? If someone takes medication they are likely taking it because it was recommended by a trained professional, therefore it probably is what's best for them-- and you are in no place to tell them otherwise. I may have never been on meds personally, but hell, I get fresh air almost every single day because I enjoy going on walks and I know for a fact that while it's nice, it's by no means a cure for depression (or at least for mine it isn't).
Something else I see a lot of going on is when neurotypicals tell us to "try and be happy," "just stop thinking about [whatever is bugging us]," "just let things go," "stop overthinking things," (particularly to those with PTSD/worsened mental health from a past event) "move on and get over it"... I could go on, but you get the idea. Like, wow, thank you, I'm cured just by you telling me to stop thinking about something! My mental health is totally 100% okay and I'll never worry about anything ever again just because you telling me to stop overthinking magically made me stop overthinking! Congrats... Except not really, because surprise, saying these things to neurodivergent folks doesn't actually cure them. Believe me, if it was that easy to actually take your advice, we happily would, but we don't actually control what goes on in our heads. There are ways to help us get it more under control, such as medication and counseling, but that doesn't magically make all our issues go away.
Perhaps the most prominent example I've seen of the issue in question is people's support for Autism Speaks. I realize I've criticized them previously but they and their supporters are literally the quintessence of neurotypicals trying to police neurodivergents. To make matters worse, people have criticized myself and other autistics I know for speaking out against Autism Speaks because they think it's beneficial for autistic people. Um. But. I'm the one who actually has autism. I think I'd know better than you whether or not my disability is being discriminated against. Even so, it shouldn't take being autistic to realize AS is a shitty company when there is literal documented evidence of them supporting the murder of autistic folks. The only people I've seen supporting and saying they benefit from AS are neurotypicals who think this just because they have autistic family members, friends, or students. But why don't you talk to the actually autistic people about it, because I haven't heard a single autistic voice support for this organization. Funny, since we're the ones the company claims to benefit, right?
So these are all examples of very clearly shitty ways to police people's mental health. But it doesn't stop there. Even little microaggressions that you may not realize you're doing might come off condescending to us. For example, telling someone that a coping mechanism or word they use to describe their mental health isn't valid or good for them just because it doesn't make sense to you. If you don't understand it, that's alright, it can be hard to comprehend something you don't have experience with. But not having a personal understanding of what might help someone doesn't make it invalid.
Or even worse, shutting someone down when they do try to explain something to you. They don't owe you any explanations of anything, but they gave you one anyway for your convenience, because they genuinely want to help you understand better why they may do certain things or act certain ways. If someone offers you detailed insight like this, you'll come across more open-minded if you just accept it rather than trying to tell them how their mental health works. You don't know the inner workings of someone's mind or whether what they tell you is valid just because you took Psych 101 a few semesters ago.
So. Now you know a few more ways not to treat neurodivergent people. Seriously, even if you mean well, we really don't like being told how we should go about our mental health by people who haven't experienced it or been trained to professionally assist us with it. You may think you know what's best for us just because you might have vaguely learned about mental health in school or live with someone who has mental disorders, but honestly, our own consciences and our therapists or doctors actually know what's best for us. All you can really do for the neurodivergent folks in your life is give them love and encouragement-- because we need a lot of that, just like any other human being.