While on night duty at Concord Hospital, nurse Edward Keegan sent an explicit photograph to his partner.
Mr Keegan then left his personal mobile phone on the desk - and the photo of his penis on the screen - while he answered a call on the hospital ward phone.
A drug and alcohol detox patient saw the photograph and, according to Mr Keegan, began to pressure him into sharing the image.
Mr Keegan said the patient demanded he make contact after discharge in September 2013 because he wanted to see what was in the photograph "for real".
The experienced nurse said the patient left several threatening messages on his mobile phone, so he sent a text asking to be left alone, along with the explicit photograph, the Civil and Administrative Tribunal heard.
"He stated that he thought if he gave [the patient] what he wanted, it would be all right and he would be left alone," the tribunal's summary of the incident said.
The tribunal also heard Mr Keegan answered a phone call from the patient around the same time.
On Thursday the tribunal disqualified Mr Keegan for two years, and would have cancelled his registration if it was still current, finding he failed to observe professional boundaries.
Mr Keegan resigned from his position after the incident came to light in 2015, and now lives in Ireland.
"In the tribunal's view the practitioner's conduct in sending a sexually explicit photo whilst at the workplace ... brings the profession into disrepute. It has no place in practice. It was improper and unethical," the judgment said.
Mr Keegan did not report the incident to anyone, make a note on the patient's record, or seek help because "he had been paralysed by his fear and he was not thinking clearly".
The tribunal said allegations the patient pressured him were difficult to assess because Mr Keegan did not give evidence at the hearings, instead relying on his interviews with the Health Department's investigators.
A peer review of the incident completed by a fellow drug and alcohol nurse said Mr Keegan became "complicit" when he did not manage the situation due to his "embarrassment and guilt".
The review said there were serious risks to both nurses and drug and alcohol patients if boundaries were not appropriately maintained.
