truscum (tru as in true?) are people you say that you need to gender dysphoric (as in, have a gender identity disorder) in order to call yourself trans
truscum are completely correct because unless you got both parts or have some disorder that makes you think you do, you are not transgender. and so in true tumblr fashion, rather than own up to being wrong and faking their internet gender bullstuff they instead resort to calling people who stick to medical facts scum