|1.||not for nothin'|
Common big house or camp preface to a piece of advice or a warning. Its use is supposed to imply the speaker is neither bossing around nor threatening the hearer, only offering sage advice or a pithy observation. In practice, however, it is often used immediately before a verbal threat to another inmate.
Not for nothin', but your cellie is a straight-up rat. I saw him talkin' to the 5-O right after that bust up where they lugged those dudes to solitary.