Coincidentally, I'm currently reading some fanfic dealing with Kirk's psychological issues in the aftermath of "Turnabout Intruder." Quite interesting take on it.
From what I read in the book Star Trek Lives!
, Shatner was quite ill during the week they filmed "Turnabout Intruder." That could have had some negative effect on his performance, but there were parts that were just stupid - like filing his/Janice's nails on the bridge, going over the top with his notion of "feminine" gestures and speech, etc. The actress was much better at playing Kirk than Shatner was at playing Janice.