Um... good question, Brittany. I wish our language was like Japanese, where there's a difference in significance when saying "I love you". Ex- "Daisuki" means to strongly like or to love, but it's not as strong and meaningful as "Aishiteru" which is meant to be said by a fiancee or something like that. To answer your question, I guess that one would say "Luff ya, bye!" in a more childish way to show less significance. Then, when you really do say "I love you", it'll be different then when you're saying goodbye. Well, that's my guess anyway lol. I could be totally wrong =p