I don't tend to call anyone "Sir" but I do say "Bye bye"! However, it is more of a "Bu-bye" rather than putting equal emphasis on both words.
"Goodbye" seems a little formal and "Cheers" (although a favourite of mine) is perhaps a little to casual, "Seeya", I'm sure, would make anyone cringe so "bye-bye" it is!
Cheers
Whirls