The presenter, who is leaving the show after hosting next month's Celebrity Hijack, said the basketball star acted like an "idiot" after being evicted from the Celebrity Big Brother house in 2006.
He said: "[Dennis] was swearing, and he’d been in a lap dancing club all night. He was a really big disappointment for me, because I’d really been looking forward to interviewing him. He’s the only major disappointment we’ve had."
He added: "And obviously Jade was one of the toughest interviews I’ve had to do, but I was glad I did it."
The 34-year-old named glamour model Alicia Duvall as the worst ever guest on the BBLB sofa, saying: "She was amazing. It was actually one of my all-time favourite episodes. She was just so unspeakably bad."
On a positive note, he listed new Big Mouth presenter Matthew Horne as his favourite guest, explaining that he had struck up a friendship with the actor after his appearance.
He said: "Kathy Burke coming on the show was fantastic, and a dream come true. Ditto Bob Mortimer."