A 42-year-old American accused of endangering the safety of an aircraft last June, claims that the whole thing is a "fabrication".
Antrim Crown Court also heard that Jeremiah Mathis Thede even questioned the decision of the United Airlines' captain to abort flight 971 from Rome to Chicago and divert to Belfast International.
Thede, originally from The Alameda, Berkeley in California, denies acting in a reckless and negligent way to endanger the Boeing 777 aircraft, or any person on the flight, on June 20 last year.
Prosecutor Gerorge Chisney said it was the Crown case that Capt Jands Latura aborted the flight over concerns that Thede's actions were distracting his crew, and which could also allow someone else to do "something in his aircraft".
Trial Judge Desmond Marrinan and the jury of seven men and five women heard that an aggressive acting Thede, one of over 200 passengers on the transatlantic flight, demanded nuts and crackers from crew members.
In addition, of the next few hours, Thede allegedly continually left his 39C isle seat in the rear economy section of the plane. He would go to the bathroom, said Mr Chisney, and changed his clothes on a number of occasions, in what he described as "very unusual behaviour".
This drew concerns from the flight attendants, who had to reassure other passengers, and the matter was reported to Capt Lature, who asked his first officer Joseph Oka to investigate.
Mr Chisney said following his report, and the fact the flight was about to leave the European landmass and continue on over the Atlantic, the Capt sought permission to change his flight plan and land in Belfast.
Landing shortly after 7pm that Saturday evening, airport police came onboard and arrested Thede. During interview the following day Thede denied the allegations made against him, claiming "they were being fabricated" and went on to question the actions of Capt Jands in diverting to Belfast.
The trial, expected to last until next Tuesday, continues.