This is what Wikipedia says about the phrase "Yabba-Dabba Doo"
Fred's catchphrase is "Yabba-Dabba-Doo!"; Alan Reed, voice actor who provided Fred's voice from 1960-1977, reportedly said that the inspiration for the phrase came from his mother, who used to say, "A little dab'll do ya," probably borrowed from a Brylcreem commercial. When the script called for a simple 'Yahoo!' Alan either asked if he could alter the phrase or he ad-libbed. It inspired, in the 1970s a short-lived fruit drink called "Yabba Dabba Dew" and may or may not have also inspired George Jetson's similar sounding catchphrase, "Hooba-dooba-dooba" (or "Hooba-Dooba"). It does, however, become the subject of a song by Hoagy Carmichael that the singer-songwriter performs in an episode of The Flintstones.
However it also says
Fred's trademark yell is "yabba dabba doo!", a phrase that was originally his club's cheer and later adopted as part of the theme song from the third series on.
Well now, courtesy of the current Flintstones comic book by Mark Russell, Steve Pugh and Chris Chuckry, it's been reinterpreted – just as the Water Buffalo Lodge is now the Veterans Of The Paleolithic Wars, so that most famous of catchphrases now has new meaning…