You probably heard it from David Chappelle's
Netflix special "The Closer".
Dyke: a word used to refer to lesbians; a term that lesbians use in gay circles; originally a
derogatory term for lesbians, now often used with pride.
Frumpy: A female with lack of concern for appearance; clothing style that usually consists of bagging; careless slothing; no style; considerably
out of shape.
So, a ''frumpy dyke'' is ''a lesbian with lack of concern for appearance, from clothes to body shape''.