Thanks for explaining the context in which this specific situation came up. It sounds like your parents tend to take his side and have an unrealistic and inaccurate view of him. This must be very hard for you to accept when first of all as your parents you would like and expect their support and second when you see how harmful and deceptive he actually is but they cannot or will not see that. In a sense they are enabling him. What happens when you speak to them about him and his behaviour?