"Bizarre behavior" refers to actions or conduct that is strange, unusual, or outside the norm. It can describe behaviors that are peculiar, unconventional, or unexpected. Full definition
After eating, they can exhibit bizarre behavior caused by a buildup of ammonia in the bloodstream. (stca.biz)
The animals were exhibiting very bizarre behavior, which a local veterinarian said is caused by a disease but not rabies. (techtimes.com)
Now I'm most certain you could also find that percentage of atheists engaged in equally bizarre behavior, what ever that may be. (religion.blogs.cnn.com)