Sadly, there is a connection between being a creep and the brain. Most of the time the creep is pretty certain of himself/herself (creeps are more often male, btw). The distinction is in the size of their corpus collosom. The smaller and less dense it is, the less communciation flows between the two sides of the brain. Since many things are perceived by each side of the brain differently, you often get two basic answers/understandings to the same question/experience. The amount of information needed to understand and see both "answers" at once is sometimes more than the connections can handle, resulting in the anxiety of being very, very, unsure as the brain tries to resolve the problem. Failing to do so, to reduce the anxiety, the person often decides one or the other is the "truth" and, to protect themselves from the anxiety, sticks to that "answer" to the point of bravado, certainty and so on.
Now the technical problem in this is a low tolerance for ambiguity, and it's most prevalent at the extremes of any group. In politics those with this condition tend to be easily belligerent and assertive with little regard for their opponents point of view. It's a defense mechanism on their part and part of the reason we are so divided.
And, as the French adverb says, "To understand all is to forgive all." Thus, you may not like them in your fellowship and they might have to be tossed out, but at least they can probably be forgiven for being a jerk.
AJ