Smiling shooter
Something you don't see often, like a smiling runner or a crying baseball player.
The smiling shooter had a big smile on her face when she unloaded both the guns she was holding.
Smiling shooter/assassin
Something you don't see often.
Your murderers might come with a smaile, but they're not usually wearing one when they kill you. Not all shooters are male, so a smiling shooter/assassin is rare in either sex.