What part of no don't you understand?

Meaning

I am plainly saying no, and I mean just that.

Origin

The phrase 'won't take no for an answer' has been in the language since at least the mid-19th century. It's included in Thomas Haliburton's exhaustively titled Sam Slick's wise saws and modern instances; or, what he said, did, or invented, 1853:

"You first of all force yourself into my cabin, won't take no for an answer, and then complain of oncivility."

(Note: Oncivility doesn't seem to be a real word - I don't know where Haliburton dug that up from.)

'What part of no don't you understand' is a modern-day rejoinder to that. It's an American phrase and the first printed reference to it I can find is in the California newspaper The Mountain Democrat, October 1988:

'He wouldn't take no for an answer,' which gave meaning to the T-shirt Jim presented Carl printed with 'What part of No don't you understand?'

The context there suggested that this was already an understood phrase and so probably dates from before 1988.

It is an example of the many phrases of a mildly confrontational nature that emerged in the USA in the late 1980s and 1990s; for example, 'talk to the hand', 'so sue me', etc.

There are many variants on the phrase and it has mutated into the generic 'what part of [insert topic here] don't you understand?'.

Whatever the source, this phrase, and its variations, have become T-shirt slogan favourites.

The phrase got a wider audience when it was used as the title of a popular country music song, written by Wayne Perry and Gerald Smith, and recorded by Lorrie Morgan:

What part of no don't you understand?
To put it plain and simple
I'm not into one night stands
I'll be glad to explain it
If it's too hard to comprehend
So tell me what part of no
Don't you understand?