Phrase meaning "what I'm about to say is important." That is "I'm not saying this for my health"....
Generally said as "Not f'nuthin', but...."
NYC/East Coast slang of the caucasian working class (particularly Italians)...
"Not for nothing, but your mom has the best rack I've seen in years...."
As a native New Yorker, it pains me to see that none of the other definitions seems to actually grasp what not for nothing means.
"Not for nothing" is used to soften the blow of something that would normally be offensive or come on too strong.
For example, if your friend showed up wearing purple and yellow striped pants to a party and asked you how he looked, you could respond, "well, not for nothing, Jimmy, but you look like a gay, retarded zebra." Or if you want to try out for a musical but you can't sing to save your life, your friend might tell you, "hey, not for nothing, but you suck at singing and you're not gonna get that part." Things of that nature.
Not for nothing, but the other guys who defined "not for nothing" are a bunch of schmucks.
Used as an introductory phrase to indicate that the principle phrase which follows is intended neither to be commanding nor officious, but simply as friendly advice or constructive observation.
Not for nothing, but you just bought the first iPad less than a year ago.
Colloquial, inverted way of saying, "for good reason," to emphasize a point. "Not for nothing is Paris called the City of Lights." Used extensively in English literature, including C.S. Lewis, Samuel Butler, and Jack London.
It can also imply consequences, for good or bad. "Not for nothing has Shaq played basketball all those years." Or, in a negative way, "Not for nothing has David Duke earned a reputation for bigotry."
It does not mean "for what it's worth," a common mistake. To see why this does not work, replace the words: "For what it's worth is Paris called the City of Lights."
There is a similar Italian phrase which is not used in the same manner in Italian, "non per niente."
Not for nothing had he been exposed to the pitiless struggles for life in the day of his cubhood, when his mother and he, alone and unaided, held their own and survived in the ferocious environment of the Wild. -Jack London
It is not for nothing you are named Ransom. -C.S. Lewis
Not for nothing is the Urban Dictionary known as the repository of online slang.
Not for nothing do Red Cross volunteers offer aid around the world.
There must be a good reason why.
Not for nothing was she named Miss Breezy Point.
Not for anything.
Not for nothing but you offend me.