I didn't realise Walliams had such a habit of pulling other men's trousers down on stage 
I've seen the Mark Ronson clip, but it turns out he's done it loads!
The routine begins with Walliams asking a volunteer to come up onto the stage and getting them to confirm their age.
When one answers 16, the controversial comedian says, 'Bingo', before adding: 'You're a big boy for 16 aren't you – that's what I'll tell the judge.'
He then kisses the boy on the lips before playing his game of 'hide the sausage', which involves him lunging for their trousers, dry humping them and leaving them with exposed buttocks and grappling to keep their genitals covered.
https://www.dailymail.com/news/article-8524613/Video-David-Walliams-humiliating-young-men-pulling-pants-stage.html