It did indeed originate from the Mongrels show (BBC series with puppets) and there's me and a bunch of UK furs to blame for it, sorry ^.^
The original plan was to have one round of OI resounding through the lobby to try and see who else saw Mongrels and would join in... and from there it kinda exploded ^.^ Never understimate a fur's capability to pick up a new trend and run with it 'til the end and beyond ^.^
But, seriously, watch Mongrels, if you can. The show is hilarious!
Seeya,
Fairlight!