Graham, That's what Ronnie Barker once referred to as, 'Pismonunciation.'
Talking of which reminds me of a little scene from 'Poirot,' where he has a parrot delivered. The guy knocks on his door and says, "I've got a parrot for Mr poy-rot."
"It's pronounced, "Pwa-ro," says the great detective.
"Oh, alright," says the delivery man. "I've got a pwa-ro for Mr. poy-rot."
My favourite, and it's not just tourists, is people who ask ridculous questions about where buses are going. In order:
A few weeks ago, someone got on the N43 southbound at Monument and asked if it went to London Bridge. Not much alternative!
Today, a lady got on the Eastbound 1 at Tesco Surrey Quays and asked if it went to Canada Water (no, and also, umm, it's right there...)
My favourite, around 18 months ago, were the group of French youths getting increasingly agitated and confused on an Eastbound N1 heading rapidly for Elephant and Castle, and to who I had to break the news that the number of the front of the bus was not the postcode for which it was bound, and it would not be taking them to Angel Islington.
My favourite, overheard while stewarding at The Globe - "That must be that Dome they're talking about" - looking at St Pauls!! and another lovely American overheard whilst walking over the Millennium Bridge towards the Globe - look there's that theatre that John Wayne built!!!