Add O'Shea Jackson Jr. (aka Ice Cube's son) to the short list of people NOT impressed by the Mayweather vs. McGregor fight ... in fact, he says it was a Titanic-level disaster.

The "Straight Outta Compton" star may have been a little biased -- remember, his dad's BIG3 had to MOVE venues because of the fight. 

It's clear Jackson ain't forgotten, 'cause when we got him at LAX he first big upped the BIG3 saying it was far bigger than they ever thought it could be, then he totally dissed the big fight.