Our end of summer term dinner and nightclub is always organised by the same person but the last one was organised with only a week to go. I let her know that I had a work conference that day and would not be able to make that date but could go on an alternative date. This did not go down well and she said in the group chat that I would be organising different date - this was without messaging me first to confirm if I could do this. I was bemused by the reaction but tried to organise for the following week but she said she could not make it and a few others had booked holidays so I left it at that. Recently I heard that they went ahead with the original date which is fine with me, but nobody mentioned this to me (I had met with some of them since and we discussed booking next year's event with more notice). AIBU to be annoyed with them for keeping it quiet?