Have known the bride for about 4 years. Got relatively close I guess through the kids but never best of friends. I offered to organise her hen do and she later asked me to do it, fine.
At the hen do she turned into someone our mutual friends didn't recognise. She got extremely drunk and abusive to several people in our group, our taxi driver got called a c@nt, and when we were separated at the end of the night she sent me a rude text.
No apology the next day, nothing. I was off with her and went home. We were due to leave that day anyhow. I have distanced myself since then. Seen her briefly out and about but haven't socialised.
We all have too much to drink sometimes it was the lack of apology/acknowledgement of her behaviour that it got my goat.
Also the wedding list annoys me - I personally have no problem with a wedding list but gift examples are an upgrade to her and the groom's transatlantic flights for the honeymoon. 
So, AIBU to develop a mystery illness and not attend? My Grandma thinks that would be wrong, but I welcome the MN jury views.