If you have the ability to have a known bad letter not be sent, then don't have it sent. That's a no brainer. I had an outlier letter from my med school EM rotation, that was totally unexpected and enough of an outlier to literally be brought up during interviews. I got this question: "One of your letters stood out amongst the others, because of how 'mediocre' it was. What do you have to say about this?" I had no clue about it until I started getting asked about it.
This was amongst a sea of universally excellent letters, grades and rotations. Turns out the $!*¥~€}%*|!! that wrote it, still decided to interview me himself, then ranked me near the top of his own frickin' rank order list.
Explain that to me, please.
When I didn't match there, everyone at that program knew I must not have ranked them at all. They all knew me since I rotated there, and told me they me ranked me very high. Apparently they ranked me high enough, they were expecting me to be a lock to go there if I ranked them anywhere near my top three.
It was very bizarre and I have no clue what it all meant, or why this guy wrote me a crap letter. It didn't hold me back though. Everything happens for a reason. Have faith. Take your punches and keep fighting, and don't let the haters hold you back.