Was the guy a pit boss from the casino next door?
But seriously, folks, you could make the case that the BRD (the Borderline Retarded Dude) is the ideal person to play BJ. Yes, he's going to lose his money--JUST LIKE EVERYONE ELSE! He might lose a bit more rapidly, but he can't even touch the -15% that some "normal" players are facing at some carnival games. Since he is a BRD, maybe he plays BJ slowly.
Here's the thing, that we can't tell without delving into his family life--maybe he can easily afford some occasional gambling. Think about it. Let's say his family is rich. They might not let BRD even handle his own money, but perhaps sometimes they give him play money to go gamble, and the casino is a safe place to send him for the afternoon. For BRD, playing BJ may be one of life's greatest pleasures! He might look forward to being at a table with other normal people, who for once don't shun him (because THEY are too addicted to BJ to leave the table). He feels connected. Maybe he gets to do this sometimes in "Fabulous Las Vegas." And, because he may not really appreciate the value of the money he is losing, he is immune to any feelings of guilt or loss after the session is over. Furthermore, his handlers are the ones who dole out the money, and perhaps drive him to the casino, so they are much more able to control any budding problem gambling that might occur, much more so than with normal people.
In fact, BRD's situation might be a powerful, heart-warming story.