Just keep on being insistent......soon they will get it through their heads to leave you alone even if it's just in kidding around. I can definitely understand your feelings.....it takes a long time to reprogram those feelings if they ever really do get reprogrammed. HOpefully you will always hold onto some sense of distance with people like that so that you will NOT get involved with anyone like that again.....so it a way, your reaction is a way of self-protection & not something that is bad IMO.