Dainichi was kind enough to tell me that よくいうよ means "to shamelessly say something you should be ashamed to say."
On spacealc, this explanation and translation is provided:
よく言うよ。 What are you saying?
What meaning does this particular よく provide, and which kanji, if any, does this particular よく derive from? (I am interested in the literal meaning of this よく from which the figurative meaning derives i.e., does it mean "talk well," "talk brazenly," etc)