>>The word "mentalist" is used over here, quite wrongly I believe, to mean a nut-case.
>>
>>eg someone picks up some dog-do in his bare hands and throws it at someone, for no reason, the victim shouts, "You're a mentalist, you!".
>>
>>Annoys me.
>>
>>I think this is a follow on from the old expression of someone being "mental" if he's crazy. (as in a "mental case")
>>
>>As for your Serbian expr., means anyone who's crazy smells of mint (menthol)?
>
>We don't have a th sound, it's pronounced as t in both Greek and English words. So "mentol" was used in slang to denote a mental case. Similarly, "hevi mental" was an expression for certain phases in the history of the heavy metal genre. That was, in turn, based on "heavy" being a slang synonim for stupid - to the point where one'd be said to be "from Trep[unspellable]a" - then anyone would know that's where the lead mine, i.e. the guy is heavy as lead, i.e. quite a dimwit. Slang often derives stuff from its own stuff. Like "where are your reindeer?" being equivalent to "how's your Alzheimer" by the following line of reasoning: "izlapeti" - lose strength by evaporation (said of solutions, smells), i.e. go senile; therefore "laponac" - word usually used for people from Laponia, i.e. the Sami, now comes to mean a senile person. The reindeer question is just the next iteration.
>
>But the rhyming slang wins hands down as being cryptic to the uninitiated :).

I presume Laponia is Lapland, in Finland, and the Sami are the Suami, ie Laplanders (or Laps).

Where is the rhyming slang BTW?

here "plates" means "feet", as in "my plates of meat", as an example.

There's an old Brit saying for crazy, only used by us who can remember pre-decimal currency - "Tuppence-ha'penny short of a shilling" (which nowadays is equiv. to c. 4p, which doesn't have the same ring to it :-)