Inspired by "The Worst Thing I Could Do" from Grease, which I personally think Santana should sing.
The Worst Thing
She has done some questionable things in the past, but, then again, there are worse things that she could do. Not that anyone else seems to think that way. But she's Santana Lopez, and she doesn't care what anyone else thinks (except Brittany.)
Yes, she flirts with the good looking males on the planet (and Brittany) but hey, she's never lied to them. She doesn't make anyone a promise she can't fulfill. She dances dirty and plays straight: she doesn't lead anyone on. Quinn's broken more hearts than she has with her "baby in the corner" act.
Everyone lies to Santana (except Brittany) and personally, she's had enough. She doesn't want to sit at home by herself any more, because she knows her father won't come home till late and when he does come home, all she'll get is a grunt of acknowledgement and a slammed door. Cold shower, indeed. So she doesn't sit at home, waiting on him. She goes out and gets drunk and goes home with inappropriately old men.
It makes her head hurt to walk past Rachel Berry's house and see her sitting at the dining table with her two dads. She's hurt Rachel in the past, but secretly, she'd love to have someone to tell her that she's worth something. Hell, Man-hands has two! (But then, Rachel doesn't have Brittany.)
Santana Lopez does not steal and she does not lie. She's not surprised that some people think she's incapable of feeling anything, but she does. Sometimes.
She can cry. She does cry. She doesn't think anyone knows that (except Brittany.) Not Puck, not the plethora of other boys, not Sylvester, not her father.
To cry in front of them would be the worst thing she could do.
Brittany is her exception.
The only one.