genderoftheday:

They’re the gender police. If you say you’re trans and don’t have intense gender dysphoria then they come to your house and write you a ticket for “transtrending”. Then they smash your lawn gnomes.

But seriously it’s short for “true transexual scum” and it refers to trans people (there are cis people who call themselves this too, but they’re actually just cis transphobes) who believe being trans is a medical condition and if you don’t have intense dysphoria, you aren’t really trans, aka a “transtrender”. They generally hate on non-binary folks a lot. They’re super racist and don’t acknowledge that non-binary genders have existed all over the world in all sorts of cultures without dysphoria (one of the reasons you don’t hear about them much anymore is cause of western colonization) for countless years.