That sounds like something my father would do... I don't know, I guess there are people who don't feel good about themselves or certain aspects of their lives, and they can not stand seeing other people succeed. I guess it's a way of projecting their negative feelings onto other people (?) like, they feel better about themselves by putting others down.
When I was a kid and my father had a rough day at work he would come home mock me until I got upset and cried... and then he would smile and laugh at me.