Needless to say more :

"Not sure how you are doing it, but you always make me smile when we are talking."
"I know how - because you are doing the same. It is then easy to smile in return."

Wish you a nice day (evening/night, depending on the timezone you are in) and if you haven't got any compliment today so far, try to give some out :)

P.S. Exceptionally, I am being positive. Enjoy it, it does not happen to me very often :D