He says the couple were not kissing, but "holding hands and looking into each other’s eyes" while they were dining.
The man, who wishes to remain anonymous, says the lack of acceptance and tolerance he encountered has disheartened him.
"We like to think of Ireland as a place where gay people are fully accepted and respected, especially since the landslide passing of the same-sex marriage referendum, but if my experience last week is anything to go by, this is still a surface image," he writes in a letter to the annual youth issue of the Gay Community News magazine
"My partner and I were in a Dublin city centre restaurant celebrating our second anniversary, and we were being physically tactile with each other. Not kissing the faces of each other or anything, but holding hands and looking into each other’s eyes.
"A waiter came to our table and told us that customers at another table were complaining about us. He suggested that we stop showing each other physical affection.
"We asked to see the manager, who said something similar, adding that he had no problem with gay people.
"When we said we had every right to show each other affection, the manager said that it was unfortunate that other customers were uncomfortable, and suggested that we leave. He told us we wouldn’t be charged for our meal.
"As we were leaving the restaurant, feeling humiliated, a woman at one of the tables, probably the one who had complained about us, said the word ’disgusting’.
"This is not the indication, on any level, of acceptance, or even tolerance. The whole experience has really shaken the foundations of what I had come to believe postreferendum about my country."
The letter has been receiving much attention online, with many social media users condemning the actions of the restaurant staff.