The condition a person suffers from when their head is wedged firmly up their ass. It's a phenomenon that affects millions of people on a daily basis, and usually results in the person saying incoherant or completely retarded things.
Dave: Hey John, did you hear about Larry from across the hall?
John: No. What happened?
Dave: He told a nun that she needed to jam out with her clam out.
John: What a fucktard
, he's got a bad case of headupassitis.