How do you roleplay an insane character without degenerating into some lolsorandumb faggotry?

I literally finished typing the word consistent, looked down, and there's my post. Good show.

Have your character have a streak of very faulty logic when doing something

Or, alternatively, your character has one field of knowledge - it could be anything from something as broad as ichthyology to as narrow as TV remote repair - and they try to apply that knowledge to anything they can, regardless of context, usefulness, or complaints from others.

>roleplaying the Joker
>not degenerating into faggotry

Which iteration?

Secondly, unless you are the DM/GM, I would advise against it. Especially in a game where you have to play with others.

Thirdly, I agree with the others. Find a mental disorder, watch some youtube videos on it, and go from there.

Paranoid schizophrenia and Antisocial personality disorder are worlds apart as an example.

If you are a schizophrenic, there is also the point that catatonia is going to eventually set in, which would make you a non-player character.

If you are a sociopath, played straight, there are going to be a lot of choices you are going to make, or not make, based on keeping your cover and not seeming like you are different from everyone else. Then you will have little impulses to do bad shit, but it's not like you are going to be pants on head retarded.

Now, mental disorders are often co-morbid, but you are still going to want to focus on one.

Oppositional defiance disorder is probably the best for someone who's trying to be chaotic though.

All in all, it sounds like you are wanting to play a stereotypical maniac though, but they are not actually that interesting or fun to be around. They just are on a constant high for odd behavior.

youtube.com/watch?v=zA-fqvC02oM

Video really shows how it can be really intolerable socially. In real life they can be CLINICALLY interesting, but to normal people they are insufferable, and even though they have compulsions to behave as they do, sometimes they have moments of lucidity and then the dread comes from the loneliness of alienating themselves.

As a character in a game, you would be just as boring/annoying for your upstaging antics.

OP here, specifically characters with legitimate dérangements. Mainly I'm talking about Malkavians from V:TM.

Oh, okay.
Pick a derangement out of the book, and then as I said, watch videos on it on youtube for inspo.

For malkavians, there always needs to be a little bit of, "I know I am crazy, but the world is fucking insane"

Use that platform to be the shaman. Call out people on their bullshit, while struggling with your own demons.
Maybe sire someone just because you feel like you can't go through the tumult of vampirism alone, especially because of the frenzy brought on by your specific masquerade.

Then fucking beat yourself up for stealing someone's innocence just because you were to scared to trip by yourself.

Feeding to gain clarity is advised as well. Play up the disquiet you feel from being hungry. The beast won't shut the fuck up until you EAT RIGHT NOW. Ooops. That was a pre-schooler.

Play some Everyone Is John, after you've kicked out That Guy out of your group of course.

Play it like Unknown Armies
Just pick some obsession or phobia and take it top the max. And go esy like "fear of bats" or "dolls"
Imagine being scared to death by glass, or sneezing (you and other), or rain. You will do ANYTHING to avoid any slight chance of encounter or occurence of your phobia.
Same with obession. In UA, some character CAN NOT miss the traffic news, or want to replace every part of their skin with someone else (but no one must know). Just do that instead of getting your inspiration from TV and comics

>If you are a schizophrenic, there is also the point that catatonia is going to eventually set in, which would make you a non-player character.
When catatonia happens varies pretty wildly. It doesn't necessarily need to happen during the game.

this.
The key to roleplaying insanity is to figure out how they would perceive the world. For example, Spazzy McWizard is paranoid, and in order to feel safe, must be on his guard at all times. Following this logic, Spazzy decides to huddle in corners, glue himself to walls, and always fight back to back, after all, why would you ever let anyone in your blind spot? Obviously, Spazzy doesn't understand why no one else seems to follow his example, and deduces that either everyone is far too trusting, or just plain ignorant.

Pretty much treat insanity the same way you treat an injury or illness.
People with broken legs walk the way they do, not because they derive enjoyment from it, but because there is something fundamentally wrong that is preventing them.

Insanity is a very vague definition but generally it means they've made a critical flaw in their logic that isn't getting corrected and affecting one or more conclusions they've made about the world. People with delusions have beliefs that have no basis in fact, but to them, it's as obvious as the grass is green, and convincing them that their delusion isn't real is akin to trying to convince a sane person that the sky isn't blue.

With some mental illnesses, such as dementia, you can think of their mind as a computer with a corrupted file recovery system.
The files and information are there but they can't always, if at all, access it when they need it and other times they could be spewing with irrelevant information and get overwhelmed by their memories.

Sometimes their mind might access information out of chronological order and they become confused about the time or place they're in or even who they're meant to be.

Fpbp

Give them a goal.

Research real mental illnesses and choose one that won't make it impossible to get along with other party members or do whatever the game's about.