mentalist

adj

1. Of or relating to mentalism

noun

1. A practitioner of mentalism.
2. (UK, slang)An insane person.

   “1997, I'm Alan Partridge (TV series), To Kill a Mocking Alan Jed Maxwell: See you next week then. We'll have that pint. Alan Partridge: Yep. Jed Maxwell: ...go and see my brother. Alan Partridge: No way, you big spastic! You're a mentalist!”

   “In front a staff sergeant with the new Royal Caledonians was gassing about Scullion and the regiment. 'And this major's a total fucking mentalist,' he said. 'What's mental about him?' asked the lance corporal beside him.”