Tesla most likely had undiagnosed and untreated OCD: He was obsessed with the number three, compulsively walking three times around a building before entering it. When swimming he would do 33 laps, and if he lost count would have to stop over before being able to leave.

Tesla was disgusted by earrings. He had to calculate the volume of his food to enjoy it. Pretty clearly he had mental issues, which is usually what the more crude expression "being kooky" implies.