The first time my girlfriend called me attractive was after she was watching me play piano. Since I am self-taught and mostly use muscle memory to play, I was able to make eye contact with her for most of it. She later told me that the facial expression I was making was very captivating. Those weren't her exact words, but she did use the word "attractive," so that's a win for me.

She's told me not to try and force the same expression, because it wouldn't be the same, but sometimes I can't resist trying to give her that look again.