I wasn't asking if Cis was an insult but if making up insults to demoralize people while you're fighting for ""equality"" is the right thing to do.
It's not, but not everyone is fighting for equality, even if there are groups fighting for equality on their behalf.
For example, just because someone is gay, they don't have to attend lgbt rallies, or protest/lobby for same-love rights. They can be gay, yet indifferent or even possibly opposed to pro-gay rights movements.
In the same way a trans individual may not care for the movement in support of trans rights/acceptance, and therefore not care about the hypocrisy of trying to belittle cis people.
Just because a person is trans (or any other minority) doesn't mean they're going to be nice. You get unsavoury people from all walks of life.