Klootzak (pronounced - Cloat-sack)...it is Dutch for ballbag...I sometimes use it as a greeting with wave and a sunny smile, much the same way as Italians say ciao, sometimes people think I am Polish or Latvian or something like that.
Failing that my choice would be Bugger - it has a lovely Olde English and agricultural ring to it, but certainly nowhere near as offensive as the C or F words.
bollocks is my favorte word, swearing or not. but if i want to be offensive, twat is particularly good, possibly better then c... as you can more easily employ it.