The TV personality was discussing a survey about the “filthiest habits” people have, which included drinking from unwashed mugs and re-wearing dirty underwear.
O’Leary said other bad habits were leaving unwashed dishes to pile up and not changing bed sheets for more than a month.
Gyles Brandreth, who was also on the programme, asked: “Who are these people?” Hammond chimed in and said: “And who’s admitting to not changing their pants?”
While the three of them were speaking, Vorderman made a guilty-looking face as she averted her eyes away from her fellow presenters.
O’Leary said: “If you’re admitting to it, you’re probably doing the sanitised version of how bad it really is, so it’s probably even worse.”
At this point, Vorderman appeared sheepish as she asked: “So how often should you change your pants?”
Both Hammond and Brandreth agreed that you should change underwear every day, but O’Leary was not about to let Vorderman off the hook so quickly.
“One of the foremost minds of her generation and this country is asking this?” he said incredulously.
“The woman who’s made seismic change at a government level, a mathematical genius is asking how often you should change your pants?”
Laughing hysterically, O’Leary fell back against the sofa, while Brandreth attempted to move the conversation along, saying: “She could’ve been saying, what are pants?”
This year, Vorderman appeared on I’m A Celebrity… Get Me Out of Here! for the show’s first all-stars series, alongside boxer Amir Khan, dancer Jordan Banjo, Coronation Street star Helen Flanagan and Olympic athlete Fatima Whitbread.
She recently opened up about her fear of drowning while shooting one of the trials on the popular ITV reality series.
Speaking to The Mirror, Vorderman said she broke down in tears for 10 minutes after filming the “Tanks of Terror” trial alongside Whitbread.