Medical info: Joker is as human as anyone human. However, over the time in the Asylum I do suspect he has built a good tolerance to chemicals. Furthermore, he seems to have an obscenely high tolerance to pain.
What's okay to mention around him: Anything, really doesn't matter. Just watch your step.
Notes for the psychics: Getting in to his head is just as simple as it would be for any other human. Deciphering it and getting out safely might be a bit of a problem.
Hugging/kissing/other non-violent physical contact: He's apathetic to and form of touch whether he acts like it or not. Hugging, kissing - both of these depend entirely on the situation and whether it'll get him what he wants or not. Since he's a control maniac, unless it was provoked by him, random displays of physical contact such as this is likely to get you a nice smile across your face. As for clingy soft of touching, he's bound to shove you off, break your limbs, and gut you like a fish. His moods vary often, however. You may be lucky with a bullet or two. Just be careful.
Maim/murder/death: Again, Joker is just as human as any other regular human. Maiming, murder, death. They're all
physically possible.
Any other questions, please comment here.