Vox Day reminds me with this piece, about women bitching at men :
Stop Telling Women To Smile
Three times in the last two weeks, I've had a woman turn to me completely out of the blue and say "you need to smile".
Yes, I know that this is a left-handed compliment when coming from a woman. It means that she's taken notice of you enough to open a conversation. She's hoping for you to continue it. She wants to continue it. She likes you or thinks you're cute.
If I could be arsed (two of these girls were a 6 at best, the other is a 7 secretary where I work - never fish off the company pier) I could have looked back at her and asked with a straight face: "Are you going to give me something to smile about?" (Sexy wink and smile at the end are optional.)
Since I couldn't be bothered, I left them with a simple: "I am smiling."