Derivative of feminoid. A foid is a militant feminist who hates men, but is constantly looking for a man to mooch off of or to support her and her eight kids.
Foid
Telling someone they are a foid means you are calling them an ass, asshole, or just that they have the big stupid. In order to show what you mean by it is putting emphasis on the F
For example:
"you foid" means big dummy or big stupid
"you Foid" means ass or asshole