A Midgardian is a Earth dweller also know as humans. This is because in Norse mythology there are 9 Realms, and Earth is named Midgard so people that live there are called Midgardians.
In Norse myth, the defensivefortress which the gods build about the middle portion of the earth allotted to men in order to protect mankind from the giants. Midgard ("middle world") is on the same level as Nidavellir (land of the dwarfs), Svartalfheim (land of the dark elves/dwarfs) and Jotunheim (the land of the giants).
Quite simply a mixture of a minger (someone who fell out of the butt ugly tree and hit the sphincter on the way down) and a fucktard (someone who isn't retarded, but who is so stupid/annoying/idiotic, that they sure do appear that way.)
Not only was that barmaid as fat an ugly as a hippo, she couldn't even subtract 4 from 10. What a mingtard!