I had a satanist roommate one time. In his free time (which was a lot, because he was a bartender) he would read other religion's holy books. That way he "was prepared" to debate them if he ever encountered them in real life. He would proudly boast that he knew more about their texts then they did. Bizarre.
Also, he was an alcoholic. He would leave empty beer bottles on the shower ledge after he showered or on the back of the toilet after he took a shit.