Well, only certain tags are mandatory, and being a bit narked is not the same as being seriously triggered (a genuine medical term for people suffering from PTSD and C-PTSD) so although I have some sympathy with you being annoyed, you can figure out it's an AU pretty fast and back out, can't you? Also, can't you tell by the summary? Personally I get frustrated with people not knowing the difference between & and / and read a fic, only to be a bit surprised when the people I thought were friends suddenly have a snog fest! Sometimes it can be just a tad annoying, but I can be sex adverse while suffering from abuse flashbacks and the last thing I want is a ship I don't even see suddenly in the middle of a fic I was enjoying! So I do get where you are coming from, tagging AU is hardly a lot of effort!