Supergirl, Season 3

Supergirl:
You think I should be grateful that you learned how to make the one substance on this planet that can kill me?

Lena:
Thousands of things can kill me, Supergirl. And everyone else on this planet. Fire, but we don't go around banning bonfires or candles. Cars kill people every day, and yet we still have the courage to get in them every morning and drive ourselves to work. There is one element on the planet that kills Kryptonians, and you can't tolerate its existence.

Supergirl:
No.

Lena:
You really do have a God complex.

Supergirl:
Do you know what it's like to walk into a room and your skin feel like it's going to be seared off your bones? Or like nails are running through your blood? That's what kryptonite feels like.

Lena:
Well, I don't know, it sounds like exactly what you need to subdue Reign.