I would just completely ignore them....your acting badly toward them may only solidify that they are being persecuted for righteousness.
Wait until she approaches you with her mumbo and then lay the freak on her. Say something like, "My boyfriend's uncle's, wife's brother is a JW and a registered sex offender. Or tell her that your afraid of JWs because they are penis worshippers or that you heard women cant wear pants and men cant grow beards, or that they are anti-education and anti-home ownership.
Or better yet... that JWs cant have oral sex and that the woman is only allowed to lay on her back with her legs sticking up in the air during intercourse.