I was reading a post in the rules forum where someone mentioned tech-priests taking an 'insanity dip'. Immediately I thought, "Who'd notice? Har har."

But this got me to thinking...

How, in an RP sense not rules-wise sense, would you approach certain characters being insane?

How would a psyker behave if he were insane vs a guardsman? Barring extreme cases (IE running around naked or eating manure) how would a GM convey to a group of players that the psyker was, in fact, crazy and not just being a typical psyker? Or tech-priest... etc?

Personally, making a guardsman or arbiter seem crazy would seem simple. Maybe they are wild eyed and mutter to themselves a lot. But this behavior for a psyker wouldn't be considered to out of the ordinary for me. And an adept talking lovingly to his data-slate and treating it like its his sibling would seem crazy to me, but a tech-priest doing the same thing would be actually par for the course.

The thing with insanity is that it isn't always immediately obvious. Crazy doesn't have to be frothing at the mouth nuts. The most interesting kinds of crazy can be just a matter of a shift in emphasis, a change of priorities. An insane Guardsman might seem perfectly normal expect for his tendency to keep his lasgun meticulously clean... until something really messes up the lasgun and he becomes totally manic about cleaning it, setting aside all other actions to make sure the gun is clean. An insane pysker who regularly mutter prayers of protection might seem normal, until he's rocking back and forth catatonic and shouting those same prayers. An insane adept might be perfectly normal, even talented and charming, until he calmly and convincingly explains events you just witnessed has happening in a way completely different from what really happened... and acts on his delusions.

I watched the remake of "Bad Leutenant" (with Nicolas Cage) recently. I think this gives some good example.

If you are found of SciFi and want a REAL "nutcase", have a look at the Firefly/Serenity series/film. The figur of River Tam is inspiring...but perhpas a little
to cute and funny for 40K

"Army of the 12 Monkey" with Bruce Willis could be helpfull. Watch the figures of Bruce Willis.

Talking about "hard to play a mad psyker":
Not really...the only problem is that "everybody knows that psykers are a bit mad". So, it only comes across if it is a little more gross.

Advise (that are not THAT "corny"):

1) Sudden swings of mood
Not like in "catatonic vs. Jim Carey" but one step before this. He could for example suddenly start to be really happy and laughing all the way...not "mad laughter" but being happy for no reason... in the 40K universe.. then, some hours later...he turns silent and broody and suddenly becomes snappy as you talk to him... only to be very fascinated with some flowers/marbles/ring some hour moments later

2) Fear & "theories"
Make him afraid of something VERY unusual. Perhaps children. He does not want to be near, he is VERY uncomfortable around them. If a pc presses the issue (hard FEL test?) he will tell them that "children are the prime candidates for daemonic possesion. They are young, their mind is weak. My mind is to strong for the daemons to crack, so they try to get me. And childrens are perfect for them.

3) Obsession
Make him obsessed with doing something. Washing hands. Scribbling some theories or notes around. Looking all doors & windows & checking them double and thrice. De-Assembling and Re-Assembling his las pistol. Every time he is not occupied with anything...and if you approach him, he "snaps back" like you would have woke him up from deep sleep.

I hope this is helpfull to you

LuciusT said:

Until he goes into a frenzy and butchers a fellow Guardsman who had accidentaly spilled some amarsec on his weapon ?

As for crazy Tech-Priests, I think the Churgeon from Edge of Darkness is a nice example of what could happen when TPs lose it.

Addtion:

Working up any other "Delusions" might be fine. The "child theorie" is just one case. It can be anything else as long as it leads to strange behaviour. The whole "machine spirit thing" is one of the cases where the !MADNESS! is established part of the society. It is just not consideres MADNESS (perhaps/because it does not interfere with social interaction/normal daily functions).

Another Example:
Make the "insaniac" believe that certain numbers are dangerous since they draw in the bad forces of the universe. You can take the numbers of the four gods of chaos here...or take numbers known to us (13; 23;) or complete different ones (11; 4;). The "Insaniac" will react very bad to anything that comes along with this numbers.

One other thing that I think can be fun to play is the insane character who is aware that he is insane. For example, being fully aware that your long-dead comrade is a figment of your imagination, but being unable to use that knowledge to make him go away. Or someone who knows that stealing is wrong, and tells himself so as he picks up the lasgun off the rack.

I am playing a character with the "From Beyond" Trait, and I have established that he, in most cases, bemusedly notes whatever emotion he should be feeling, but does not actually feel it. Leaving him free to follow or ignore the path that a normal personwould most likely take.