Before his trip, Leigh Van Bryan wrote that he was going to "destroy America".
He insisted he was referring to simply having a good time - but was sent home.
Trade association Abta told the BBC that the case highlighted that holidaymakers should never do anything to raise "concern or suspicion in any way".
The US Department for Homeland Security picked up Mr Bryan's messages ahead of his holiday in Los Angeles.
The 26-year-old bar manager wrote a message to a friend on the micro-blogging service, saying: "Free this week, for quick gossip/prep before I go and destroy America."
The Irish national told the Sun newspaper that he and his friend Emily Bunting were apprehended on arrival at Los Angeles International Airport before being sent home.
"The Homeland Security agents were treating me like some kind of terrorist," Mr Bryan said.
"I kept saying they had got the wrong meaning from my tweet."
This has gone too far.
