Just something we say

There are verbal solutions that we all fall back on.  A lot of people end almost every sentence with "you know what I'm saying?" or some variation thereof. 

You will find that if you answer them ("Yes, I do!") they are as surprised as the guy who lit a match to see how much he had left in the gas tank.

There's a new one going around. I think it was first popularized by Donnie Wahlberg in his sensitive portrayal of NYPD detective Danny "Danny" Reagan, who spices up his accusatory speech with "not for nothing."

As in:

"Not for nothing, but why were you carrying a two-foot sword on the subway?"

or

"Not for nothing, but I think you're guilty as hell."

(No one is ever innocent as hell, you know? Not for nothing)

Wahlberg said it a lot, and now I am seeing others do the same.  Just the way everyone on cable news answers a question now by starting with the word "So..." That replaced "Basically...."

There is a debate among linguists (and these become high-pitched, I assure you) as to whether "nfn" is a literal phrase or an idiomatic phrase.

I think it's both.

In the literal sense, here's an example: "Not for nothing, he had thought to pack jumper cables in his trunk, knowing his battery was unreliable."

And the idiomatic (slangy or trendy) sense: "I think you need to stop and buy me a hamburger. I'd appreciate it, not for nothing."

Idiomatically, it's just something to say to fill up space while waiting for your hamburger.  Gotta run, see you tomorrow, not for nothing.