The tycoon's rant came after Cohen shocked other stars on the red carpet when he turned up as his latest role, The Dictator, and dumped the powder over Ryan Seacrest.
Incensed Trump said security at Sunday night's event should have put the Brit comic "in hospital."
Despite E! host Ryan seeming to take the gag well, billionaire businessman Trump claims he was "visibly upset."
He raved: "This third-rate character named Sacha Baron Cohen thought he was being cute and funny when he threw ashes at Ryan Seacrest.
"Now I know Ryan Seacrest and he's a great guy, and you could see that he was visibly upset. It's disgraceful.
"And the security guard that was standing to the right — he ought to be fired immediately."