When I was in Australia in 1995 I remember being in a surf shop where, it turns out, ‘bearded clam’ t-shirts could have sat nicely next to Frankie Boyle’s range of Parched Spaniel yoga pants. Two guys were in the shop, looking at a Mambo t-shirt ‘Map-o-Tassi’ printed on the front, and laughing.
They had to induct me into the cult of understanding that ‘Map-o-Tassi’ was a euphemism for a lady’s ‘down under’ (another euphemism).

Back in the UK, I spotted a surf shop in Bristol has donned this name, Mapatasi – and wondered if it was from the same joke source, and it was.

Once more, unless you know the code you cannot unlock the joke.