It looks completely stupid and retard to me.
A sexy expression to me would be either an honest smile, or that almost-angry "I'm wild and out of your league" look that top models give in photo sessions.
Absolute boner-killer. Although I do think it's hilarious that girls make that face on pictures, see the pictures, and still fail to see how it makes them look retarded rather than hot.
Nope, when kissing, there needs to be another person present. If you do it to the camera, it doesnt look good.
In very rare cases like the girl in the first picture is cute, but most of the times is just plain stupid.
I don't do it myself, but I find it very hot.