Top ad man Jonathan Disegi created a sickening scene at Bergdorf Goodman’s posh restaurant when he arrived “completely loaded” at lunchtime and vomited on the bar and other horrified customers.

Award-winning ad exec Disegi, who is Commonwealth/McCann’s executive VP, global director of strategy and research and leads the company’s Chevrolet account, staggered into Bergdorf’s packed BG eatery alone Saturday after 2 p.m. before vomiting all over the bar and splashing other well-dressed guests.

In a scene even too extreme for the hard-drinking habits of “Mad Men,” witnesses said of Disegi, “He came in alone and seemed already completely loaded, leaning over and slurring to female patrons eating at the bar. He looked and sounded like he was rolling into an Irish bar on St. Patrick’s Day.

“Jonathan was bragging to strangers around him that he was in advertising. He seemed totally obliterated. He kept ordering drinks. At one point, he got up to go to the bathroom, and women who were eating at the bar complained to the bartender, asking them not to serve him anymore, because he was so drunk.

“He returned, sat down, and then he threw up all over the bar. He put his head down, and it splashed on the counter, dripping on the floor, and onto a woman’s expensive Burberry jacket. Staff rushed to clean it up with napkins.”

The witness said Disegi — just like Don Draper coolly slinking out of a cocktail bar — paid the bill, got up and strode out of the restaurant. The witness added, “The smell was terrible.”

At the time, BG Restaurant was packed with guests including a few top female media executives, shoppers and patrons arriving for the afternoon tea service. The restaurant did not respond to a request for comment.

Disegi, a regular patron at BG, admitted to us via email Sunday, “Yes, I had too much to drink. It was a mistake. Publishing this would not be good for my career, and I really beg you to be discreet here. I made a mistake, and I feel terrible.”