Greetings from the UK.
On the podcast you guys sounded really surprised Brendan Gleeson says to Oliver Platt "I think you are a mental" (or something along those lines). I was very confused, as in the UK, that's a completely normal turn of phrase.
One who is "mental" (verb) is "a mental" (noun). Its a short hand term for "a mental patient", one who resides in a mental institute.
Also, on another note, I was watching Community earlier this week and saw a very handsome man who I didn't recognise... until he started shouting excitedly and I realised it was the one and only Jason Mantzoukas.
