Wouldn't be caught dead

Yes, it is. 'I would not be caught dead (by anyone) picking my teeth in public.'

'I wouldn't be seen dead...' is quite common too.

I read the phrase slightly differently—so e.g. 'I wouldn't be seen dead in that dress':

'Even if I were dead, and therefore in a condition where pride in my appearance had no further meaning, I would still refuse to wear that dress.'

(There is indeed a hyperbolic aspect to the idiom.)

MrP

Hello Paco san

The non-physical sense of 'catch' is as you surmise; but it usually also implies that the person 'caught' would rather not have been, e.g.

'I caught my son looking at a very dubious website last night.'
'His wife caught him with the au pair.'
'I caught him smoking behind the bike sheds.'

There are other 'catch' idioms:

'I caught up with Peter last night' - 'I finally got hold of Peter for a chat last night'.
'I just caught the last ten minutes of the football' - 'I just managed to watch the last 10 minutes of the football'.
'He caught me one round the ear' - 'he hit me over the ear'.
'He caught me a fourpenny one' - 'he hit me quite hard' (usually in the eye).
'You'll catch it!' - to a naughty child: 'you will be punished severely when someone finds out!'

MrP

Hello Paco san

They make sense, but the 'caught' gives the action in each case a particular tone:

1. The son affects to do no work at all for his exams, and would have been horribly embarrassed to be caught 'swotting'.
2. Her grandmother is clearly still an attractive woman.
3. He'd been telling everyone he'd given up smoking.

An 'au pair' is indeed usually a girl. The phrase has curious implications. Every English male brightens at the thought of employing an 'au pair'. He can hardly believe his luck if his wife suggests it. When he tells his friends, they will make inappropriate comments, in which he will bask happily. Both he and his friends will spend a great deal of time discussing the likely physical appearance of the prospective au pair. Traditionalists will hope for a 'Swedish' au pair. (This category includes any Scandinavian type.) Modernists prefer the more southern European variety. The latter are considered to be more likely to wander through the house in a state of undress. Their personal morals are also assumed to be more lax. (It goes without saying that the au pair is expected to wreak havoc in the family home.)

In reality, of course, the wife of the male in question chooses the au pair. His hopes are rarely realised.

I have a dim recollection that 'fourpenny one' may refer to the cost of the beefsteak applied to the black eye that ensues. But I wouldn't swear to it.

MrP