5. The Hangover: Part II (2011)
This is probably the first film that anyone thinks of when they think of unnecessary sequels these days. After the surprising success of the first instalment, then this was bound to happen. I really wish it didn't. Somewhere in this mess of a movie, the characters actually sort of acknowledge that this is just a retread of the first film with the line, "It happened again." It really did happen again, pretty much exactly as the first film played out. Only that this time, the Wolf pack were in Bangkok instead of Las Vegas. I wouldn't have minded this sequel if they had just tried something different as there is still some mileage left in the characters, but that wasn't to be. The jokes were cruder and more mean-spirited to compensate for this, making this an utterly distasteful affair. Grossing a total of $581,464,305 worldwide, then the third instalment is currently being produced as I type this list. I just hope they try something different.