For me it is the poster who needs proof for every little statement. In my experience, over time this kind of poster grinds any discussion to a halt because they get locked on the "where's my proof?" even if it is over something nonsensical like "monkeys flew out of my butt." Sarcasm and joking seem to both fly completely over their heads. They also generally like to take 20 mins to an hour away from a thread and then come back and ask for said proof again, even if the discussion has moved on from the subject in the timeframe.