For what it's worth - I'd also make sure that this "user ID" is NOT your actual primary key. Because it carries "user significance", and like Jeff pointed out, because this fields is a violation of normalization by combining multiple data elements, this thing is BOUND to change in the future (Just wait until they want to have MYNORTHCHIN and MYSOUTHCHIN, and "split" the MYCHIN group in half). Do NOT make this your actual PK, or you will have a maintenance nightmare on your hand.

Let them have any user ID they want if you can't convince them how stupid it is, but for goodness sake, just keep is as a surrogate key. Manage your own key, and insulate it from any stupidity they might come up with.....