The dictionaries usually define bunfight as British English slang for an elaborate party or social do.
"Bunfight: a grand formal party on an important occasion"
- World Web Online, http://www.wordwebonline.com/en/BUNFIGHT
It seems a rather antiquated working-class word for a posh do. Working class people didn't throw bread-rolls at each other, but they were only to happy to remember it when the toffs do.
The more modern meaning is:
"(UK) A formal but friendly tea party held by an organisation either annually, or to mark some occasion"
Nowadays the Bunfight is an annual event which is always great fun for everyone attending, young or old. It is held on the last Saturday in November, traditionally at the California Ratepayers Hall, Finchampstead"
- Berkshire Bedlam Morris dancers. http://www.berkshirebedlam.org/Bunfights/bunfights.htm
But the word is seldom used in either of those senses in the press. The more normal use of "bunfight" seems to be that of an elaborate and prolonged argument, something that could have been a simple negotiation turned into an ongoing unresolved dispute, with overtones that the dispute has a life of it's own beyond the original reason for dispute. A flame war without the internet.
Here are some examples pulled up on google of the usage:
"F5 starts patent litigation bunfight
Application switching firm F5 Networks this week filed suit against three rival firms after securing a patent on a key aspect of its technology."
- The Register
"...in academia the literary canon is less a list carved in stone than a trampled battlefield where a perpetual bunfight rages."
"The debate has sparked a political bunfight, with Mr Brough's criticism of policing in communities prompting a threat from Northern Territory Chief Minister Clare Martin to boycott the summit."