I honestly don't get why some people view this almost as if it's a crime against humanity.
... why is it so offensive to refer to a trans person as the gender they don't identify as?
I would just see it as unnecessary and bad manners. It's like telling someone that she has a really big nose and she really ought to see a plastic surgeon or someone at the gym that they shouldn't bother since there is no way that some weed like them is going to look anything other than a total wimp.
Perhaps you do do those things. Perhaps they make you happy. Why? What difference does it make to you to call someone "she" or not tell Miss Pinocchio that she has better streamlining than an F35?
If someone wants to have long blonde hair and wear lipstick, what difference does it make that they have had an operation and the contents of their underwear have changed? They are probably not my type so I'm not going to check anyway!