A blind man.

[moonraker558]

A blind man went for a job in a wood yard saying he could identify any wood by its smell. They tested him on different types & he guessed right every time. To catch him out the secretary laid naked on the floor with her legs open. He sniffed & said he wasn’t sure & asked for the 'wood' to be turned over, he sniffed again & said: "You can't fool me, it’s an old sh1thouse door off a fishing’ boat!

[magicmerlin]

Or 'the sh1thouse door of a Grimsby trawler'