1. A less-profane, more whimsical way of referring to a clusterfuck.
2. A situation involving a large amount of confusion, disorder, or mayhem-- usually with many people present.
Attributed to the Wes Anderson film "Fantastic Mr. Fox" (2009). In the film, "cuss" replaces curse words in the main characters' speech, thereby allowing dialogue that is humorous and emphatic but still appropriate for younger audiences.
Having clustermers come in can be a store-owner's dream-come-true if each of the members of the group buys a few items, but it can also be a nightmare if they all just want to use the restrooms.