A demiguy is someone who only partially (not wholly) identifies as a boy or man, whatever their assigned gender at birth. They may or may not identify as another gender in addition to feeling partially a boy or man.
Demiguy pride flag created by transrants[1]
Alternatively, demiguy can be used to describe someone assigned male at birth who feels but the barest association with that identification, though not a significant enough dissociation to create real physical discomfort or dysphoria, or someone assigned female at birth who is trans masculine but not wholly binary-identified, so that they feel more strongly associated with “male” than “female,” socially or physically, but not strongly enough to justify an absolute self-identification as “man".
The original coiner of demigirl/demiguy is unknown.