It's passive aggressive stuff and you don't need people like that in your life. Some people think its clever to be disrespectful. Unfortunately family members will say things to other family members that they wouldn't necessarily say to strangers or friends. Family dynamics, say for example a sibling being jealous of the other might use this passive aggressive stuff against the other because it makes them feel powerful in some way. There can be a variety of reasons for it... being nasty for the sake of it, is just one of them.