Cis annoys me as well as its often used in a derogatory way along with the fact that, as you say, woman or man is perfectly adequate to describe someone who identifies with their birth gender. Im actually quite sick of it being labelled. If you choose to identify differently thats your choice. I find it baffling coming from the generation that pushed for gender equality and the idea that gender doesnt define you etc that suddenly its so important that people get upset that they arent the other gender.