During sex, participant A sticks a slide whistle up the anus of participant B. Participant B must then expel gas through their anus, hopefully making the slide whistle make a sound. If performed correctly this will sound like the character 'Tiny Clanger' from the iconic British children's TV show Clangers.
"How are you enjoying your new slide whistle?"
"It is great! Last night I was doing my wife and I gave her a Tiny Clanger."