Charles and Jemma Rangi were dining at the Heritage Hanmer Springs on Saturday night when Gilmore's group arrived.
Mr Rangi immediately recognised Gilmore, who was accompanied by Christchurch lawyer Andrew Riches and their partners.
"We were sitting about 5m from them. Right from the beginning, pretty much [from] when he [Gilmore] walked in he was already being quite arrogant - whistling at the waiters and clicking his fingers to get them over there to give them more drinks and stuff like that," Mr Rangi said."It was quite awkward, the restaurant was nice and quiet."
Mr Rangi said one of the women at the table was also "being quite vocal".
"Right from the get-go they had about three or four bottles of champagne ordered, it was all just sitting there. I don't know if he'd been drinking before he came into the restaurant, he looked fine when he came in.
"But he had that arrogant persona about him right from the start.
"We left before it really kicked off by the sounds of things, but it was really quite awkward."
Mr Rangi said he was not at all surprised to hear that Gilmore's "unpleasant" behaviour worsened.
"The staff there were being so professional about it. I made a comment to my wife at the time that if he'd been treating me like that I would have been telling [him] where to go.
"You wouldn't expect to see anyone behave like that - let alone an MP," Mr Rangi said.
Soon after Mr and Mrs Rangi left, Gilmore allegedly called a waiter a "dickhead" when he refused to give him more wine.
Gilmore then gave the waiter his business card and reportedly said: "Don't you know who I am? I'm an important politician."
