Totally agree. I always say please and thank you, and I can't remember any FA not acnkowledging my appreciation.

I have always found it odd that he or she is thanking me for throwing my trash away. In my mind, I am the one who should be thanking the FA for bringing me the bag to get rid of it. (And I do, so the exchange is "thank you!" "thank *you!*")

I don't think it's a F or otherwise issue. It's a single person issue, and I've noticed it all over the place. (Like kids on Halloween, but I won't go there.)

As someone said, it's just good manners. Not everyone has them.