how to deal with people who think they know everything??

My father-in-law is like that. He is in debt up to his eyes, overweight and the doctors have told him he'll die. He knows nothing about computers, but if I go over, he'll tell me (me!) how to use the computer, tell me what I should be doing to get out of debt (I owe £500 on a credit card) and tells me that I'm not eating healthy (I'm the right weight for my height). I just want to scream, but I keep quiet as he's family now.

I have this problem at work so everytimethe person starts totalk I walk away.I know this bothers him but he knows not to bother me with his nonsense.

I have a standard reply to unwanted advice. I just say "Thanks for giving me your opinion. I will take it into consideration." I am also careful to be aware of who is listening if I want to complain.

I really don't like when people have this beleif that they know everything. I would politely tell them, I really am not looking for advice on my life I need to figure things out on my own but I appreciate you trying to help.