deadly smile

1: A smile so ravishing, glamorous, or beautiful, it could kill you.

2: Smiling so hard that it hurts.
3: Smiling so hard that you feel you are going to die. Ex: Doing a portrait photo shoot that lasts an hour.
4: A sinister smile that is full of evil. ex: The Joker played by Jack Nicholson as well as in the Shining.

5: A smile that is lifeless and lacks happiness despite being a smile.

"Jack Nicholson gave a deadly smile in The Shining."
"My girlfriend gave the most deadly smile when I showed up with flowers and she was wearing that sexy black dress. My heart just stopped as I gazed at her beauty."
"At the end of that 2 hour photo shoot, we had the most deadly smile ever (because it was killing us or because it no longer looked real)."