Well he didn't try to save her life, he did it to scare Klaus. What's more unforgivable is how he did this, this whole situation on the bridge where her parents died. That was probably the worst.

By far this.
The one with Damon is also bad but he did it because he wanted his brother. I understand that.
Letting himself being a ripper....well it happened. Thank writers he had, and still have everyone on his side to be good again.

This moment was horrible.
But I don't forget that he killed Andie,too.

I'm not a fan of any of those actually

I think all of these are pretty bad, but this one was the worst. At first I couldn't believe that he would do that.

Yes, this one is the worst. But I still love Stefan and this didn't change my mind, at all.

+ Forcing Damon to complete the transition, both were cruel

This