A war of words between a disgruntled customer and a restaurant owner has spilled online, after the customer posted a nasty reply by the restaurateur on Facebook.

Mr Arun Ratnaa, 28, had written an email to Mr Ken Lim, the owner of Don Quijote Spanish Restaurant at Dempsey Road, on Saturday, after he and a group of friends were supposedly turned away at the door even though the restaurant was "far from full," he said.

Mr Arun got a rude reply containing an expletive instead, which he posted on his Facebook profile on Monday.

On the same day, Mr Lim, in a strongly worded reply on his restaurant's Facebook page, said Mr Arun's post did not give the "full facts", and that his staff "was at no point rude to (him) and in fact apologised several times that (they) were not able to accommodate (him)".

Mr Lim also said he took issue with the fact that Mr Arun had signed off his email as a fellow food and beverage industry professional, and not as a diner.

"If you had written to us in a personal capacity, I would (have) bestowed every courtesy that is bestowed on all our customers." he wrote.

The exchanges has since been liked and reposted hundreds of times.