"I was having a coffee with a client at 4 Millbank last week. At the next table were a couple of guys in their late thirties. One – an American – was going on about how awful Gordon Brown was – so dull that he couldn’t get his editor to carry anything about him. The other guy – a Brit – replied (more or less verbatim) – “yes, I know, he sucks the life out of everything – that’s why at the BBC we call him ‘the Dementor’”.
You have to be a Harry Potter fan to get it but it is a perfect description!
I'm not a Harry Potter fan, but it seems apt to me!