Derangement, demeanor and behaviors.
Like all Malkavians, Irres is clinically insane. The official diagnosis would be schizophenia along with tendencies of fugue, but these terms often fail to summarize his experience and behaviors.
He constantly hears voices in his head; some offering him extraordinary (almost prophetic) insight, and some just invading his thoughts with irrelevant, random messages. As a result of that, his attention span suffers greatly, and so does his thought process; which, to an outsider, seems chaotic.
Being a schizophrenic, he may alter between compassion and empathy to the exact opposite in a blink of an eye, and often, his displayed emotion does not correspond to the context he's in. The simplest way to explain this is that he perceives emotions as a mere act which he performs so well that he manages to convince himself. Sometimes.
When he's having fugue he's very good at stealth, lockpicking and generally finding himself sneaking into all sorts of places he shouldn't have. He has no memory of the deed however, nor how he got there. When not in fugue he doesn't even remember which key to use to open his locker; let alone lockpick his way into a top security establishment. He just tends to come around, find himself at a completely unknown environment and sneak his way back out, while confusedly trying to figure out what happened in the meantime.
It takes a lot of discipline to maintain an inconspicuous appearance when on duty, and for the time being Irres manages to evade suspicion, by dampening the ruckus in his head as much as he can. He is aware, however, that the more time passes and the more he uses dementation, the more often his ability to conceal his derangement will fail, until he won't be able to work anymore and he will have his Sire's fate: being transferred from asylum to asylum as a common madman.
Besides exhausting his willpower to muffle the voices in his head when in the presence of mortals, Irres has picked some tics and nervous habits, like constant fidgeting, biting his nails and incessantly humming to himself. When he's on his own he spends hours having fully-fledged conversations with the voices in his head.
Still, using so much willpower to keep up appearances at his workplace means that he has none left for other occasions; so, unless you are one of his fellow coworkers, you will be met with the full extent of his madness.
Overall, to the mortal employees and patients of the asylum, Irres appears to be a quiet and reserved professional, who does not talk much, has a few perculiarities, has a soft spot for the asylum's 'lost cases' and only works at night. To everyone else, he appears to be a jolly -to the point of creepiness- lunatic.
As a doctor, Irres had always been favored by the psychotic inmates of the asylum because he always showed empathy and respect that the other doctors didn't. Unlike them, he had the patience to sit with them and listen to their thoughts, opinions and wishes. Since his embrace, however, he became so popular with these patients that they refused to cooperate with anyone save him, claiming that "this doctor gets my meaning!". His colleagues were delighted by that turn of events and eagerly passed these patients to his exclusive care, as they viewed them as a nuisance and had given up on them long ago. The rest of the inmates (meaning those who still maintained some semblance of sanity) however started avoiding the eccentric doctor like the plague, whispering that there's something eerie about him.