The Britain’s Got Talent judge is asked to help out, and it isn’t soon before long he is wearing full protective gear including a fetching union flag helmet.
In a first-look clip, a nervous David can be seen on stage being told to “stay still” whatever happens.
Even Ant and Dec take the opportunity to wind up their pal by offering him a protective bowl to cover his “crown jewels”.
Cheeky Jack rides around the best-selling author getting dangerously close to him with his bike.
Britains Got Talent’s David Walliams
But the horror didn’t stop there for David.
Jack tells the judge to lay down and it’s safe to say David’s face was a picture.
What tricks does Jack have up his sleeve and can he pull them off?
Recalling the moment, the Little Britain star revealed: “It was quite scary because I had never seen that guy before. I mean, I’m assuming he’s good at what he does! I was told that I had to remain completely still so I couldn’t really see what was going on, because all I could do is just stare up at the ceiling.
“It was quite scary because I didn’t really know what he was doing, but I just put my trust in the show that I wasn’t going to get hurt. I mean, I just guessed that if the producers were up for it then there was a good chance he wasn’t going to hurt me.”
Britain’s Got Talent continues Saturday at 8pm on ITV. If you’re looking for more to watch check out our TV guide.