Euphemistic Double Entendre

This is the kind of silly thing writers lose sleep over:

The other day my cousin posted on Facebook:

John: Time to make myself extremely unpopular with the neighbours again! Grinding out my pointing!

To which I replied:

Me: Hope you're not grinding out your pointing in public, cous. Don't know about complain, you could get arrested for that!

To which he said:

John: There are no euphemisms being used at this time Maz! 

To which I was about to reply, but didn't:

Me: Euphemisms or double entendres? 

To which I then found myself trying to answer my own question.

Just for those who aren't sure (thanks to Google's 'define' function):

eu·phe·mism 
/ˈyo͞ofəˌmizəm/

Noun: A mild or indirect word or expression for one too harsh or blunt when referring to something unpleasant or embarrassing.

And:

dou·ble en·ten·dre 
/änˈtändrə/
 
Noun: A word or phrase open to two interpretations, one of which is usually risqué or indecent. Humor using such words or phrases.

In this context, 'grinding out your pointing' is both a euphemism for 'having a wank' (which is in itself a euphemism for masturbating) and, in the same vein, a double entendre, because it has both a euphemistic meaning and a literal one. It's possibly moreso a double entendre as it has a specifically risqué and indecent application.

I then started to wonder whether all double entendres are euphemisms, though not all euphemisms are double entendras? But that isn't right either, because some double entendres are simply grammatical mistakes, such as the example: let's all eat grandma (let's all eat, grandma), or miners refuse to work after death (miners refuse to work, after death).

But then, doesn't that make this form of double entendra a pun?

pun
pʌn/
 
Noun: A joke exploiting the different possible meanings of a word or the fact that there are words which sound alike but have different meanings.

So, are all puns double entendres, and most double entenres also euphemisms, except when they're grammatical? And are euphemisms only ever puns when they're double entendres?

It was about this point that I saw the article Metaphor, Simile and Analogy: What’s the Difference? and gave up thinking forever.