mouseburger
A woman of no particular intellect or attractiveness.
... mouseburgers — people who are not prepossessing, not pretty, don’t have a particularly high I.Q., a decent education, good family background or other noticeable assets — can come a long way in life if they apply themselves. I am a mouseburger and I have applied.
Where it comes from
mouse + -burger; compare earlier nothingburger. Coined by Helen Gurley Brown by 1970.
Adapted from the Wiktionary entry mouseburger (CC BY-SA 4.0).