The origin of the name Wittertainment lies, primarily, in a discussion that spun off the film Blood Diamond - and therefore probably that movie's most lasting impact on popular culture. It is a story in four parts:
On 15 December 2006, listener Tony writes in to say "you'll get through all the reviews if you don't witter", in response to the fact that Mark Kermode was continually leaving reviewing the film he would name as his Movie of the Week until the end of the podcast, and thus was not having any time to talk about it (Shortbus had been a particular victim of this). Simon Mayo replies that wittering was "kind of what we do."
On 26 January 2007, Mark reviews Blood Diamond, describing it as "issuetainment". This is a word he has derived from Danny Baker, who used to refer to his eponymous show as "infotainment at its most infotaining". It is also a word Mark has previously been used when reviewing Happy Feet.
Mark's use of the word results in various listener contributions on neologisms and other portmanteau words, and listener (William) pointed out that "issuetainment" had a precedent in "genutainment" on The Day Today, in which viewers' films of real accidents were used in a segment called It's Your Blood.
Thus, the "-tainment" riff is established.
At some point in the week after the Blood Diamond review, a page appears on Wikipedia under the name "Wittertainment" - defining it as:
"A term inspired by the Good Doctor, Mark Kermode's film reviews on Simon Mayo's BBC Radio Five Live show.
Suggested usage: Wittertainment at its most wittertaining.
In a nutshell, Kermode, the barrel-chested former Queen's guardsman is provoked into ranting by the urbane and erudite Mayo, a perfect foil for the discontemparily-coiffed Kermode. The ensuing witter is surprisingly entertaining. Kermode is undoubtedly a man of many words, a small few of which he unfortunately uses very often. These include, and indeed are exclusively limited to: Guillermo Del Toro, Ken Russell's wife, tertiary syphilis, and some movie called The Exocet, I think.
However, for dedicated pod-casters, Kermode and Mayo cause time to pass unnoticed, a not inconsiderable but much appreciated feat while driving in contemporary urban Ireland."
Although the Wikipedia page was deleted shortly afterwards, the word stuck, becoming shorthand for the Film Review Show itself. Its use has also spread to the show's social media presence, particularly the hugely income generating Wittr app and it's lesser clones Twitter and Snaptat.
The new strapline for the show is to be one of the following: "2 'til 4. 5 Live. Wittertainment. Incomprehensible British banter."
"This is Wittertainment on 5 Live. Stretching defiantly optimistic maxims to well beyond their limits for more that 12 years."
Simon talks about the Wikipedia page to Mark on the 2 February 2007 show, somewhat perplexing Mark, but nevertheless entrenching the word "Wittertainment" in the listening consciousness.