An offshoot of the onomatopoeic word "boing," the phrase "Sha-Boing BOING!" is used as a confident emphasis at the end of an assuredly correct statement. This is similar to other phrases such as "Yeah, that's RIGHT!," "That's what I'm sayin'," "You said it," or (in more spiritual settings) "Can I get an Amen?"
Emphasis is put on the second "boing" and the gusto with which that "boing" is delivered is meant to underscore the sincerity of the speaker's resolve that his/her statement is the undeniable truth.
This phrase is especially useful after successfully completing an act which others have claimed impossible.
Speaker 1: "There's no way you can dunk from that far away."
Speaker 2: "I can & I will."
(Speaker 2 successfully dunks.)
Speaker 2: "Sha boing BOING!"