It was the 21st 30th birthday of me and SIL2. SIL1 sent hints for two weeks before "is it alright if your DB and I still come around even though SIL2 can't make it?" (first I'd heard of SIL2 not being able to make it.). Few more of these hints. I ignore. Eventually contact SIL2 who says they're talking crap, of course she's coming. They then tell SIL2 not to come to her own birthday party because she couldn't drink at the time, and wouldn't be fun. Abs remains reasonably calm apart from whinging to DP constantly about this.
Abs goes off, buys all the supplies for the party, gets ready, cleans etc. etc. (I know! I cleaned!) A few hours before I am going to be uncontactable etc., DB contacts me and goes "so sorry. We can't make it. our dog-sitter has bailed. No one else on the planet is remotely able to look after a dog. What a tragedy, our life is awful etc. etc. we're just going to stay home and cry ourselves to sleep". I then go mental at him, DP goes mental over this, my MOTHER goes mental over this.
Come the day, they rather sheepishly turn up (turns out the dog sitter could work after all) but NOT WITH THE GIN THEY PROMISED TO BRING.
I know right? There's so many things they did wrong, put their dog ahead of family, try winding people up, lying, generally being annoying but worst of all they didn't bring gin. Pah.