This overheard is from the summer of 1980, during a family holiday to the south-west coast of England when I was about 11 years old.
We were at the beach on a beautiful, warm and sunny day. Myself and my sister (aged 13) were enjoying ourselves rowing about on our inflatable raft on a very calm sea, about 30 yards from the beach. Nearby were three people in a small speedboat with an outboard motor, one girl and two guys, all late teens to early 20s. The two guys on the boat were being rowdy and clowning about, diving off their boat into the sea, swimming back and climbing on again. We could overhear them talking and shouting and they had brummie accents, which is the accent of people from around Birmingham in the midlands (think of the accents of the members of the heavy rock bands Black Sabbath or Judas Priest, your Rob Halford's, your Ozzy Osbourne's - classic brummies). Anyway, myself and my sister were trying to ignore them, but after about 10 minutes we overheard the girl on the speedboat shout out in panic to one of the guys in the water "Roy, Roy, mind the propeller Roy!". Me and my sister burst out laughing. Fortunately, no limbs were lost and the phrase "Roy, Roy, mind the propeller Roy!" became our catchphrase for the rest of the holiday.