When he was an apprentice at the shipyards, Billy Connolly was sent to get "the equipment from the Stowaway's Locker". He was given rough directions to a distant part of the site and advised to get further directions there. Long story short: events took their course, the coin eventually dropped, Billy confronted his workmates and they pissed themselves laughing at him. End of joke.
A little while later, one of his team asked him to get some corundum powder. Corundum is natural aluminium oxide, a very hard, white, crystalline mineral, used as an abrasive in many industrial applications. But Billy had never heard of it, and thought that it sounded like the most stupid joke name going. To his workmates' bemusement, he told them that they weren't going to catch him out again so easily or so soon, and refused to go the stores.