Why does everyone, especially Emma and Rylan, on BB seem to answer every question with 'do you know what......' It drives me absolutely crazy now grrrr

Linguistic contagion. It happens a lot within the Big Brother house too. I've accidentally found myself watching BBUK 2005 (after someone posted a clip on here) and by the end of the series it was practically mandatory for housemates to start their sentences with 'at the end of the day'.

Because it gives the impression that whatever they are about to say is profound.

That's true. It's a casual way of providing emphasis.

Yes they did!! Everybody used to say it all the time.
I do expect better from presenters though. Emma seems say it every time she sits on that couch talking to Rylan on eviction nights. When Rylan asks her how it went, she sits back puts her arm on the back of it (her 'yawn' trademark position) and says 'do you know what....'

"I ain't gonna lie", is another prejoinder loved by the Essex fraternity.

Do you know what? I often do that - I don't know why It's just been part of my way of speech since I was a kid. I perhaps don't use it as often as I once did but - do you know what - I sometimes still use it

It's all coming from the Essex towie lot another one is you know what I mean after every thing they say they can't pronounce anything staring with th they always pronounce it F example fink fought fumb etc etc drives me mad they sound so fick,(sorry couldn't resist)