Combrination of "femcel" and "doomer".
Femcel is the female equivalent of an incel.
A doomer is someone who already gave up on life, listens to sad music and constantly tired.
A foomer is a femcel girl that has accepted her faith but is not happy with it. She wears black, has a pimpled face, bad odour, and a hopeless future.
Don't be such a foomer! You can still be a nice catlady or something.