Bill's right. There actually are no "rules" around this joint, but I think that the consensus is that "BS" threads are the ones that are pure goofing-off and stuff that has nothing to do with music. Some people object to the goofing off and want a forum that's just about music - so Max created a filter to sort out the "BS." If you put muswic information or lyrics in a "BS" thread, that defeats the purpose of the "BS" designator.
-Joe Offer-