Dictionary.com says that

Pun.
1. the humorous use of a word or phrase so as to emphasize or suggest its different meanings or applications, or the use of words that are alike or nearly alike in sound but different in meaning; a play on words.

I had a conversation with a friend recently.

Me: Want to go XXX next week?
Fren: Who's going?
Me: John and frens
Fren: So interesting (pun intended)

After this, we enter into a argument discussion about what whether the statement "Sounds interesting (pun intended)" is a pun. To me, it's just sarcarsm. Pun should be a clever use of words to instil a second meaning to the sentence. To him, just as long as he say there's a second meaning, it's a pun. In this case the "(pun intended)" is what makes the sentence a pun. Not in the clever use of words.

Maybe I am too narrow minded to accept it. I just can't agree that it is the correct ways to brand a sentence a pun.

He go on to tell me that this brand of writing is common among writers/journalists in lifestyle pages because they think the word sarcarsm is too offending, so they use the word pun instead. I can understand the meaning behind it now, but I still say it's the wrong way of doing things. If the writer is worth his salt, he should be using a real pun and not use "(pun intended)" to instil his hidden meaning.