A lot of pubs have two names, the 'official' name that's on the licence and sometimes on the sign outside, and the colloquial. I used to go to a pub near the assizes in Norwich which everyone knew as The Murderers, but I have no idea what its 'real' name was.
Another was the pub under the old Daily Mirror building off Holborn Circus where many of the hacks would go to drink and grumble. Officially 'The White Hart', everyone knew it as 'The Stab'; as in 'the stab in the back'.
My local is called 'The Ramp' - no idea why, because the real name is (I think) 'The Miners'
Corruptions of existing names seem to occur all over the English speaking world, from the Mucky Duck and Brass Cat already mentioned to numerous others. I used to frequent a folk club held at 'The Lady of the Lake', which was known locally as 'The Bitch in the Ditch'