The term "asshat" has its origins on the forum for cruel.com. It can refer to a person who posts a topic that had already been posted before, or to the duplicate topic itself, or to the act of posting a duplicate topic.
If a cruel.com poster noticed the duplicate subject they would typically add a brief message to the thread containing the term asshat.
1. Nice asshat! (referring to the act of duplicate topic posting)
2. This is an asshat. (referring to the duplicate topic post)
3. You, sir, are an asshat. (referring to the poster of the duplicate topic)