I've been diagnosed with Complex Post Traumatic Stress Disorder - which is what most of the characters with 'PTSD' that I've seen should be calling their disorders. The different is that PTSD tends to stem from one major event, or potentially a handful of similar events, whereas C-PTSD is from repeated traumatic instances such as childhood abuse, abusive relationships, sexual abuse, human trafficking, living in a warzone, etc. I understand that it's just because people aren't really aware of the difference, but a quick google can tell you there is one. It's just frustrating to see people claiming their characters are diagnosed and it's - unless this is a key plot point - wrong as hell.
So many characters I've seen don't actually exhibit PTSD symptoms either, they're just scared of stuff which is a valid way to respond to trauma but to get diagnosed with PTSD you have to experience more than that as a symptom. There's actually like, so many things you need more than that. Like, a lot of the characters I see here have a bit of The Sads and have panic attacks. Now, I am definitely not saying that that's not valid cus it is - but it's not PTSD. It's frustrating to watch people who don't seem to do any basic research outside of 'one time I saw this character who was like this', and it really doesn't take that much work. Below is a list of PTSD diagnostic criteria.
A stressor - the traumatic event.
Intrusive symptoms - at least one - thoughts, nightmares, flashbacks, etc.
Avoidance of trauma-related things.
Changes of thought processes and such - at least two - forgetting the trauma, overly negative thoughts about self/world, high-key blame of self/other for trauma, isolation, disinterest in regular activities.
Changes in actions - at least one, but most people with PTSD that I know have two or three - higher irritability/aggression, increased risky behaviour, hypervigilance, difficulty relaxing/sleeping/concentrating.
It's all got to last for more than one month, have actual impact on your life and relationships - and if you're not diagnosable until six months after the event, you've got 'delayed PTSD'.
I'm also diagnosed with BPD - borderline personality disorder. It's horrific. I hate living with it, and it's more damaging to my daily life than my C-PTSD. But the only characters I see with it are the... well, super-fast-bipolar-axe-murderers or the hyper-manipulative-evil-genius characters. Also a lot of people seem to mix up bipolar disorder and borderline personality disorder, there's... so much wrong with that. I'm just so used to BPD being used to signify that this character is 'clearly evil' and 'awful' when in reality everyone I know with BPD is struggling to keep themself in check all the time because they care about other people too much.
The last issue that really digs into me personally is ADHD. I have ADHD and it's the woooorrrsssttt. I constantly talk over people, I get distracted when people are talking to me because I'm focusing too much on listening to them talk to me and I don't process what they're saying, I am bored ALL OF THE TIME and I cannot bring myself to do basic chores like cleaning and washing because they're not FUN and don't give me the dopamine boost I need. It means that even when I'm doing well, my room is a tip. I have a million unfinished projects. My friends think I'm a flake because I forget I agreed to do stuff with them. It's not just all quirky and happy and fun-fun-fun. It's hard and a struggle and I NEED characters to display this side of ADHD too. I know that the fun bit is the public face, but even just... a character coming home to a sink full of dishes would be enough.
I'd also say a pet peeve of mine is labeling people for the purpose of like... creating a list to prove how messed up the character is. Like. Some things are comorbid, and I understand that because like, comorbidity between C-PTSD and BPD and such. But, some people will just slap diagnoses onto their characters with no thought about the symptoms of those things and how they should actually be affecting the character. You can't say your character has X without giving them the symptoms of X.
...oops that was very long.