Try shutting up
Well…
It’s not exactly a slur, true, but it is nevertheless highly objectionable, and not just to the person being called it. It assumes matters not in evidence – it assumes that there are “cis” people and “trans people” when in fact there are only people. Cis would not mean anything without the existence of the word “trans” but the word “trans” names something that doesn’t exist. We don’t need the word “cis” because it’s just the equivalent of real or actual or non-fake. Trans women are real, actual, non-fake men. Trans men are real, actual, non-fake women. It’s simpler to just ignore the fakes and go on knowing which people are which sex the way we always have.
“Cis” is not exactly a slur, but it is a specialty word that exists to legitimize the war on women that trans ideology is. No I’m not going to “try this” when the “this” is pretending there are two kinds of women, fake and real.
…thus changing the topic from sex to gender identity, from biological (fe)males to people who think or feel is certain ways best left unspecified, are in possession of an invisible, undetectable, undefinable, indescribable, inexplicable, inscrutable (fe)male soul or essence etc., while at the same time turning the statement into a claim about what’s going on inside other people’s heads. Either that, or “cis women” relate to “trans women” the way fruitbats relate to baseball bats, i.e. not at all, it’s just a bad pun.