Rob Kardashian Off the Hook for Alleged Threats Against Pilot Jones

Rob Kardashian did not make criminal threats against one of Blac Chyna's alleged side pieces -- or at least there's not enough proof he did ... TMZ has learned.

Law enforcement sources tell us the L.A. County D.A. rejected Pilot Jones' criminal complaint against Rob. Pilot claimed Rob sent him threatening texts when photos surfaced of Chyna and Pilot kissing.

We're told the case lacked sufficient evidence to move forward. As we reported, law enforcement sources told us the alleged threats, made last October, were "murky and general."