Pepper Plants Twisting
Why do some of the leaves on my pepper plants twist so that they are upside down?
Certified GKH Gardening Expert
This is caused by a pest typically. There are a few that it could be, such as broad mite, aphids, whiteflies and others.
Treat the plant with a insecticide. I personally like neem oil as it is safe for people, pets and good bugs as well as being effective. Here is more information on it: