At best, misgendering a person is disrespectful; but when done deliberately, knowingly — it is always an act of violence.
Mistakes are made; which is not the same as asking trans communities to tolerate them. The truth that many do, with grace and tact, does not dim the cis privileged ignorance on display. Check yourself. Check your ignorance. Also if you have ever used to the word, cisphobia — you are just a straight-up idiot.
Go read this wonderful post by Trananarchism.
If you want to be a good ally, you need to start taking cissexism and transphobia seriously right now. That means getting our goddamn pronouns right and not expecting a cookie for it. That means learning our names. That means not asking invasive questions or telling us how well we “pass.” (Passing generally means “looking cis.” Not all of us want to look like you, thank you very much.) That means deleting the words “tranny” and “shemale” from your vocabulary. That means understanding the immense privilege you have in your legally recognized, socially approved, medically assigned gender.
Seriously, stop everything — Go read the full post now.