The term itself "Lost Faith in Humanity" means nothing anyway.
Lost your faith that Humanity what? That Humans are good, or kind, or gentle? I've faith in Humanity to act as Humanity does: In whatever way they feel they can get away with that makes them feel good.
You can't "Lose Faith in Humanity", that would mean you NO LONGER BELIEVE IN HUMANITY. Now, Humanity, when not attributed to another entity, can't be an abstract concept, so you meany you no longer believe in either the attitude of humans, or humans themselves. That's crazy, and you should probably seek help. If you've lost faith in Humanity's humanity, then you're a bit odd, since you define the abstract concept humanity, by something other than the attitude of Humanity.
So basically, you should say what you've lost faith in. I assume you mean Humanity's capacity for kindness, but I could just as easily insert, Humanity's Cruelty, and make you into a puppy hater.
Finally, as many have pointed out: One evil woman kills puppies. What does that say about Humanity, and why do you exclude yourself from your epiphet? Why does her killing puppies reflect badly on me, but not you (The lack of attack on self is implied by the statement, by saying I, you pass judgement, meaning you consider yourself morally superior). How does it reflect on anyone? We all come from a species that brought about Hitler, has made countless species extinct, and created Ke$ha. Why is this worse than any of those?
Now me, I'm a misanthropic asshole, but don't pretend you can get sympathy by acting all misanthropic and juvenile because you saw something that offended you. I'm a misanthrope because I dislike (most) people. You're playing at the misanthrope because you lack emotional depth.