From Everyday Feminism - though I still reckon the site is a satire site.
everydayfeminism.com/2017/04/cissexist-say-never-date-trans/
Anyway, in summary - basically if you don't date trans folk, you are 'cissexist'.
'So if we look a little deeper into this issue, there’s the possibility of your genital preferences being at least somewhat partially informed by growing up in a cissexist society. There’s also the fact that a preference is different than saying you would never do something.'