[HPforGrownups] question for any Brits re. slang in DH

[Jennifer]

No: HPFGUIDX 174821

Hey everyone, I am still fairly new and have been
mostly lurking but thought I could pose this question
to any UK list members:

There is a term that was used a few times in DH which
I recognise (from Buffy's Rupert Giles) as being an
insult, but I don't really understand it's meaning;
"Berk". 

Can someone explain exactly what this means? Your help
is greatly appreciated.
jen

  ~Jennifer
   
  Tea is wealth itself, because there is nothing that cannot be lost,
  no problem that will not disappear, no burden that will not float away,
  between the first sip and the last.
- Henry David Thoreau