Question: If you made a statement that after you realized you made a pun and it wasn't intended, why excuse yourself (by inserting 'no pun intended') and leave the pun there?
That is like warning people that you're gonna fart, do it, then say sorry when you had every intention of doing it. Except, you weren't aware that doing it could bug anyone but that you are not liable because you warned them. They they have any problem with it is irrelevant; you were gonna fart, that's it.
I do it all the time and I do excuse myself cuz everybody does it.
Technically, you should not be aware you made a pun to then say it wasn't intended. To put them in the same sentence...just sounds like laying trip wire and telling people that there is trip wire there, but if they fall, it was not intended.
I'm not compaining, I just see it as funny cuz it seems backwards.