Hey wesbottom:
Your contribution is a new angle on this discussion. I could see how it could be a thrill to let loose in casual situation, only you knowing what's going on beneath the baggy pants.
In a similar vein, I know that there is a web site, but I am not able to locate the URL for it at this point, that sells those things with the pitch of them being useful for beer drinking men who go to football games and don't want to deal with leaving the action for a piss. My recommedation for that would just to have urinals right by the stands, but we know that that won't happen in the U.S. anytime soon.
This same website also show pictures of drinking guys standing around mardi gras using the male urinal of which you speak WITHOUT the benefit of the bag. One guy casually has strolled up to a storm drain and lets loose!
This website always make me scream with laughter:
http://www.bumperdumper.com.
MIL