Truth be told, putting in "F***" instead of the actual word is just annoying; we know what the word is, so simply say it or don't. Since you are not going to use cursing, I recommend fake swear words. Think Monty Python French Guy:
"You don't frighten us, English Pig-Dogs!"
"Go boil your bottoms, you son of a silly person!"
"Your mother was a hamster, and your father smelt of elderberries!"
And so on.