While the web is buzzin' with the Epic Beard Man's fight on an Oakland bus, (which is unshowable on Neatorama for obvious reasons if you've ever seen it), I prefer this one: when koalas fight, as seen on Robert Gale's A Welsh View blog.
What - you think that koalas are cuddly and cute all the time? Link [embedded YouTube]
The sounds are a little disturbing.