Well... is a sexy guy, the term goes from Tumblr, where girls used throw panties and bras to the johnas brothers.. whatever is the name written..
and with the fandom, many terms became popular such as the Tumblr sexy man, which stands for ; a guy from a famous (or not) fandom, needs to cover mostly of these characteristics.
Being tall, and white.
Dress well, by defect with suit or elegant, with a soybean complexion physique, being a main villain or known one.. or just having a bad side.
Even though the criteria varies, like for example, sans from undertale is mostly consider a tumblr sexy man, bill cipher too!.
And they might be goes for categories.
"Gosh he's such a Tumblr Sexy Man"
"Who?"
"Bill cipher"
"girl go get some therapy ðð"