That was Uncle Leo's signature greeting for Jerry.
Did you never watch Seinfeld?
I know knucklehead...the Hello however should have had a ? after it as Jerry says this to Uncle Leo as he gets arrested for the books. Because in that same episode Uncle Leo gets mad at Jerry because he sees him but doesn't say hello. Jerry is the one who turns him into the bookstore and Leo gets pissed saying Jerry how could you and Jerry says hello?
Hence Buzz's next quote...
Don't ever question my Seinfeld knowledge...I will take you on anyplace anywhere in Seinfeld trivia...jerk store.