Today's BWOTD is one your lovely old granny might use:
"Oh fiddle sticks, I made a total mess of that!"
'Fiddle Sticks' = substitute for any cuss/swear word
Basically if you don't like to cuss or are just too well mannered to do so, then you need to know this word if you ever visit the UK. Because everyone will understand that you are effectively cussing, even though you're not!