"Frumpy Dumpkins" is a generic name used to describe the "ugly girl" that wants to be hot in any society. "Frumpy" is used to describe her fugly, lumpy, or bumpy self while "dumpkins" is implying that she is the type of girl you'd dump or find in a dump.
There also used to be a clothing line at frumpdumpkins.com that is stylish clothing for the not so stylish female.
"Look Zach is hanging around ole Frumpy Dumpkins
over there in the quad."
I got my new shirt at Frumpy Dumpkins house last Wednesday!
That girl is a lil frumpy
& a lil dumpy
so she is Frumpy Dumpkins.