Can I say, "Bless You" to our Catholic priest? Our priest does such a great job at our church. I shook his hand after church and said "Bless you".  I meant to say "Bless you for all you do", but was it offensive to bless a priest?
"Bless you!" is short for "[May God] bless you!"
So, you are not blessing a priest, but asking God to.