1) Any "get together" of human primates where alcohol is involved, and there is a nearly complete lack of female human primates.
2) More generally, a social gathering that the person using the term does or did not find pleasurable.
This expression was conceived on the patio of a bar in Sudbury, Ontario, Canada called "Cactus Pete's". A friend of the inventor's commented that this bar sucked, and why did we always go there? The inventor of the word (henceforth referred to as me), exclaimed, "Yeah, this place is a sausage fest. No, wait, it's worse. This is, like, a sausage factory, where they manufacture the meatiest and juiciest sausages, like Johnsonville Brauts!...This place is fucking Johnsonville!"