A MHG is someone you see, that you think is hot, but didn't get a good enough look, so you have a little bit of doupt.
Girl 1: OMG, look! look!
Girl 2: what? who is he?
Girl 1: he's an MHG that's in my science class.
Girl 2: no girl, he is foe sho HOT
Girl 1: really?! sweet! im talking to him tomorrow!