To be the innocent bystander or victim of an explosion, either pyrotechnic or as the result of an instantaneous release of pressure, ie. a pressurised vessel bursting.
'Whatever's the matter? You look awful.', 'I'm sorry. on the way to work I was firthed!'
'My god. I've been firthed!'
When you are shafted, done over, ripped off or stitched up for no apparent reason or benefit to either party
God dam it! I was just finned!
Did you just fin me????
Don't fin me, man!