For me it's probably:

"Don't you do it
You're not even you yet"

I first heard Otep's Perfectly Flawed when I was early in transition and deeply suicidal. I'd already been hospitalized for it a couple of times. And then I heard this song and felt like it was speaking right at me. I'm still alive. Still depressed and working on it, but alive with the intention to continue. I don't know if the song actually helped or if it was all the other things I've tried, but it still resonates fondly for me so I'm comfortable calling that lyric my favorite.