He is grateful that he is hung and hairy like his dad.  He is grateful that his dad lets him eat his hairy ass whenever he wants.  He is grateful that his dad likes to eat his ass, too.  He is grateful that he and his dad also like to lick each other's hairy balls, suck each other's big dicks, and swallow each other's loads.  He is grateful to be a man, just like his dad.