A term that can now not only be used to describe someone bitching at ya and telling you what to do but also to describe something that is great or chill or cool or dope or whatever... so yeah, preach on.
person 1: I just bought a dope cruiser bike at the thrift store so now im set for the summer
person 2: preachin' brutha!
friend 1: Shoooot me need practice my engrish today
friend 2: wow thats a preachin' idea