Actually, even HL has been known to use the F word at home. It's extremely rare so I know something terrible is happening when I hear her use it.
It sort of starts like this: "Oh.........F***!" .............5 second pause....."O-o-o-oh F***!" ..................10 second pause.................."Oh f*****kety f****kety f***!"
Usually it's something really awful like she's burned the toast or something.
Englishman.