MIL bought DS9 and DS4 new bikes for Christmas. Well, it would be more accurate to say she paid for new bikes. She got her son (my BIL) to actually make the purchase (fair enough as he gets a discount) and then asked me to collect them from the shop yesterday (not something I was chuffed about as I had a million and one things to do, had to borrow a car as mine was in the garage, and didn't have anywhere to hide them at ours). Ended up taking them to my DM's who is bringing them up later today along with her own presents.
MIL has just been round and told us how disappointed she is that the bikes weren't here when DS9 and DS4 woke up. I told her she should have brought them herself then. Honestly I wasn't in the mood to be made to feel like I'd done something wrong when I'd actually done more with her gifts than she had. She replied "I didn't want them to be from me, I wanted them to be from Father Christmas." DS9 looked up at her a bit WTF - he has had a few moments of doubt this winter but last night and this morning was fully enthralled in the magic, and now she's just dropped that clanger. Unphased she simply pointed at DS4 who was oblivious to it all as he was playing with his new toys and said "He doesn't know." Oh, well that's alright then if you've only given it away for one child.
I took her to one side and reminded her that DS9 still believed and to try not to give the game away. Her reply was "well he'll have to find out soon." Not your fucking decision though is it?! 
So AIBU to be utterly fucked off with her attitude and her quite possibly giving the game away to DS9. I'm aware that he was having doubts and that this may have been his last year of believing so I may be a bit U but if anything that made me want to savour the magic even longer and I've got that WTF look of his playing through my head and feel like my heart broke a little bit seeing it. 
tl;dr
MIL ruined Christmas