Here's a common affirmative defense: Plaintiff’s claims are barred in whole or in part because Plaintiff harassed Defendant for the debt in violation of the law.

This means the plaintiff should lose because they harassed you and violated the FDCPA. 

This defense is backed up by Federal Rules of Civil Procedure Rule 8(c)(1): "Estoppel."

This is one of the defenses you can make in the SoloSuit Answer.