It was Defcon 6 if I'm not mistaken and someone actually didn't go because of it which is how it became a meme.
Here's at least one source corroborating that[0]:
> "I think it's from around DC6 and is a reference to our only near brush with cancellation at the Monte Carlo for DC4," Def Con spokesperson Darington Forbes wrote me in an email. "I wish I had more to tell you—since it happened seventeen or so years ago my info is murky. Something about a casino mogul preferring we not use the Monte Carlo, threats of legal action."
> @ivydigital DEF CON - cancelled annually for over 20 years
