Daniel Radcliffe hitting Diana Rigg with the condom was pure hilarious.
VLAD LOVES UNDERAGE BOYS JUST LIKE HIS DADDY USED TO.

Some people suggesting Bowie but I don’t think Bowie is being ‘nasty’ as such. He just carefreely creates a song inspired by the person he’s just met, and is too self-absorbed to consider how devastatingly insulting it is. He’s not actually
trying
to hurt Andy.
That said, it might rank as the most savage scene in the show. Bowie is literally singing ‘chubby little fat man blows his stupid face off’. Gervais’ reactions are so good you actually worry if Andy is so traumatised by his failed pursuit of respect that he might actually take his own life.
The show superbly balances comedy with agonising cringe, but this scene dips into real darkness and is mildly disturbing.

Clive Owen definitely

De Niro was probably playing himself,or very close.Compared to the other celebrity appearences he has very little time onscreen so harder to assess.Thought Samuel L Jacksons onscreen persona in the episode he was in was fairly neutral.His reaction to Maggies rant about jazz is probably about what you'd expect.

The celebs were better satirized in the first series, whereas in series two it just boiled down to everyone acting like @ssholes.

re Bowie yes he starts off as extremely nice/approachable ("I cant hear you love come on over here") as many have said Bowie was in real life.. and then listening to Andys problems almost in sympathy ('things not going too well eh'). but then that 'little fat man who sold his soul' and then the almost 'man who fell to earth' faraway look as he turns to the piano and we realise hes just listened in a very detached way using this fat pleb Andy and what hes telling him about his crap show for the basis of a seemingly throwaway song to entertain the partygoers! (as Bowie was known to have eccentric ways of coming up with songs/lyrics).
perhaps it was especially devastating to Andy as he (like Gervis in real life) may have been a huge Bowie fan and is of that generation.. then again he didn't seem too bothered about Bowie beforehand when they were sat in the 'VIP section' so maybe not lol

Jonathan Ross was the biggest tit and he was playing himself

He seems like such a nice guy in it at first and then he just starts humiliating Andy and its just so vicious what he sings!
Yes, this is it.
You kinda expect high profile actors to be buttholes, someone like Ben Stiller has probably had a bad mood at some point and been a jackass to some fan in real life, and stories like that never get off the internet.
But David Bowie? He's instantly likeable. That's why it came so out of the left field when he goes from sympathetic listener to extremely mean bully.

Yes I was LOL. Sorry to resurrect this old thread, but I also wanted to add David Bowie to this list.
His sad death made me think of his brilliant appearance in this. God he was hilarious. He seems like such a nice guy in it at first and then he just starts humiliating Andy and its just so vicious what he sings!
"Little fat man has sold his soul, chubby little loser!"
LOL what a dick! He had brilliant comic timing here Bowie. Shame he didn't do more comedies RIP.

Wasn't he playing a character though? I thought the OP was referring to a celebrity who played (a version of) themselves.
You don't choose the soy sauce, the soy sauce chooses you.

It wasn't Clive Owen, it was Jonathan Cake.
It's not "sci-fi", it's SF!

I think it probably was Clive, and kudos to him for putting himself out there for us to have a giggle at. A lot of actors probably have too much pride to let themselves be seen that way, even though we know it's just a script. I liked Ross Kemp as well, cuz he's such a hard-man with his Afghanistan tv stuff, it was funny to see Vinnie Jones challenge him like that.
You don't choose the soy sauce, the soy sauce chooses you.