How to deal with an immature uncle?

I'm in my 20's and my uncle in law is in his 60's. He's retired. My mom and I live with him. He always compares himself to me. He likes to bluff a lot, he says that he can do things better but he's actually a wuss. Everything that I do he always has to say that he's better than me, then starts laughing. He studies me and keeps an eye on everything I do, always trying to find my weak points. Basically he's not happy every time I accomplish something. He acts like this when there are other family members around, but when it's just me and him he tries to be nice and sweet talks.

I don't understand why he has to compare himself to me and always have to say that he's better. Why does he watch my every move, and try to find my weak points? Why is he targeting me at all?
How to deal with an immature uncle?
Post Opinion