"He initially refused to, but then said that he wasn't able to, which is hard to believe. Security staff were then called."
Airport police were notified and the man was removed from the flight after it taxied back to the terminal.
An airline spokesperson said the matter was now in the hands of police and it would not be commenting further.
However, the man was not arrested and the aircraft departed for Cardiff with a slight delay.
The Irish Independent also reported that last year, a drunk passenger was removed from a Dublin flight after he asked a flight attendant for sex.
He was said to have removed his clothes shortly after take-off and waved his genitals at other passengers, before asking a crew member for sex.
The Sun Express flight was headed to the Turkish resort of Izmir, but had to divert to Belgrade due to the man's behaviour - where police were waiting at the airport.
- nzherald.co.nz