I'm pretty certain
Imbecile is a genuine technical term.

As for the rest, well - subnormal, retarded, mentally deficient - these were the PC terms in the 60s, which is where these are from.

Edit: Still pretty amusing though.
( The Light in Chains don't touch the Pope's boner, Tue 9 Jun 2009, 20:10, 2 replies, latest was 17 years ago)

I'm 40 honey, and remember such vocabulary was the norm when I went to school
The irony for me was finding such a book list on a modern website. IMHO political correctness is a pain in the clopper - it's gone way too far. A few years ago, we weren't allowed to refer to black boards or white boards, but had to call them chalk/pen boards. Now we have these new-fangled interactive white boards and suddenly they're called white boards again. wtf?
( Tourette's ( . )( . ) has a monkey hair in her fried egg, Tue 9 Jun 2009, 20:17, Reply)

just checked that link
I'm still chortling ;o)
( Tourette's ( . )( . ) has a monkey hair in her fried egg, Tue 9 Jun 2009, 20:19, Reply)

The order is weird
I would have ranked them Idiot, Moron, Imbecile from smartest to dumbest but a moron is way smarter than an idiot.
( The Light in Chains don't touch the Pope's boner, Tue 9 Jun 2009, 20:31, Reply)