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4.
By the use of this phrase to open or close a statement, the user acquires or asserts a pleasant, folksy authority. Sometimes paired with "boy" for added authority and folksiness (see example).

Frequent famous users include Cris Collinsworth and Hank Hill.
"Boy, that was a heck of a down field block by Michael Vick, I tell you what."

"I tell you what, the Seattle Seahawks came here to play tonight."
by TebowTime23 January 19, 2012
 
1.
chiefly southern, esp texan. added at the end of pretty much anything, esp to add exclamatory sense to a clause. has a somewhat cryptic meaning known only to southerners. so you non-hicks, stop trying.
Bill's car is so red, I tell you what!
by yuan January 06, 2005
 
2.
Something Gary Whittaker says to either begin or end a conversation.
"I tell you what, that beagle is a power dog." - Gary Whittaker

"I tell you what, one time I ate 5 gallons of ice cream in one sitting" - Gary Whittaker

"I was at one time, the fastest man in Ohio...I tell you what, was the fastest white guy down at state." - Gary Whittaker
by Maynard Yoh February 07, 2012
 
3.
A phrase commonly used by people in the South. Can be used in the beginning or end of a sentence. Common to Texans, it is used as a whole sentence, with nothing before or after it.
Bill Engvall talking about Texans: "Man, I tell you what."
"What?"
"I told you."
by Nicolee February 07, 2012