"I was standing at the bar waiting to get a drink and I wasn't expecting it," he said.
Guildford is in Rarotonga for the wedding of rugby mate Jarred McCarthy, who plays for the Napier Pirates Rugby Club, and his fiancee Sam Barlow. The couple will marry on the island tomorrow before a large group of family and friends, including All Black Israel Dagg.
In September, Guildford admitted to a drinking problem and met with All Blacks coaches to promise he would take steps to control his drinking.
But the Kiwis watching him on Friday night say his behaviour was appalling.
Fiona, an Auckland woman also celebrating a birthday with the same group of Kiwis in Rarotonga, said Guildford was extremely drunk.
"His eyes were gone, he was completely out of it," she said.
Fiona said she and her two daughters were shocked to see Guildford stagger drunkenly round the bar.
One of her daughters and her boyfriend had been thrilled to realise they were on the same Auckland to Rarotonga Air New Zealand flight with Guildford on Wednesday night. But the daughter later went on Facebook to say their "completely defenceless" 60-year-old friend had been "blindsided" by a drunk Guildford.
After assaulting Cox, Guildford climbed up on to the bar's stage, Fiona said.
"At that stage he seemed to realise he was naked and tried to cover his penis."
Restaurant staff rushed to wrap an apron round Guildford's waist as he bolted into the kitchen.
A group of Guildford's friends came in looking for him and hustled him out the back into a carpark, his naked backside still showing through the gap in the apron, she said.
Cox, who lives on the Sunshine Coast, said he did not plan to lay a formal complaint about the assault but, referring to Guildford's drinking problem, said the All Black had "an issue that he needs to sort out".
He wondered if Guildford had possibly mistaken him for former All Blacks coach Graham Henry. "I'm 60 and bald and I think Henry's the same."
Another witness said Guildford appeared "completely psychotic".
Trader Jacks staff member David Tautu said he didn't care that the drunken man was an All Black. "I was just trying to get him out of here. He was naked and bleeding and he got into a scuffle at the bar."
Junior, a barman at Trader Jacks, said the mostly Kiwi crowd began to turn on Guildford, shouting "You're a f***ing embarrassment, you're an All Black" and other profanities at him.
Both Tautu and Junior said the police were called and showed up shortly after.
However, Cook Islands police yesterday said they had received no reports of indecent exposure that night.
Earlier in the night Guildford was drinking with the wedding couple at their villa on Muri Beach.
Barlow said she was not aware of an incident at Trader Jacks. Earlier in the day Guildford had picked her and McCarthy up from the airport. He was not intoxicated when he left their villa but she did not remember what time that was.
When told he had been bleeding at the bar, Barlow said he had fallen from a scooter earlier.
* Did you see what happened? Email us here.
- Additional reporting: Cook Islands News
