Angry Traveler Punches Out Airline Agent at Airport Gate, on Video

A Maryland man wasn’t exactly flying under the radar after throwing a lethal punch at a United Airlines gate agent -- and the turbulent experience, including his arrest, was caught on camera.

Take a look -- 54-year-old Christopher Stuart Crittenden lost his cool over flight delays at Dulles International Thursday, screaming, "I’m done with this bulls***" ... before apparently launching a shocking swing at the gate agent who was blocking him from boarding.

The punch was so intense it sent the gate agent crashing to the floor, and you can hear the stunned gasps of bystanders before the clip cuts off.

In other footage obtained by TMZ, Crittenden shows zero remorse, screaming "United sucks!" while being cuffed by police and led away -- prompting cheers from onlookers.

A fellow passenger tells TMZ the guy was already heated after his first flight got canceled, the next one was full, and even though he finally snagged a seat on the third flight, he was still pissed over the delay.

When the gate agent tried explaining things, Crittenden lost it, allegedly swung at him, and reportedly even tried to go behind the counter to take a swing at the pilot, before getting tackled.

The Metropolitan Washington Airports Authority’s fire and rescue department told TMZ the injured gate agent was transported to a local hospital.

United Airlines issued a statement saying that Crittenden -- a retired Montgomery County Fire Department Captain -- has been banned from ever flying with the airline again.