A whole lot of things haven't worked for me (esp. when I was relaxed), but by far the worst product I've tried since going natural is Giovanni Nutrifix. I only used it once. My hair isn't protein sensitive (I actually do protein treatments at least once a week) but I swear, after I rinsed this stuff out, it was like I could SEE the cuticles in some strands all raised, rough and tangled with the other raised, rough, tangly cuticles of some of my other strands!
Of course I couldn't actually see that...but at the time, I swear...
I can laugh at it now because my hair bounced back rather quickly, but I will never touch that stuff again.