crackpot + madhouse.
'Pothouse' was a word coined, I think, by Ginger Barwick - Bravado merchandiser and wide-boy to the stars. I can only assume it comes from a mixture of 'crackpot' and 'madhouse' and is used to describe those of a slightly unstable nature.
There you go folks. First-class, grade A example of a pothouse. Bad spelling and all.........;-)