The relationship between Brody and Patrick is the closest of the entire series. Due to their families being good friends for over twenty generations, it's not shocking at all to discover that they have been best friends ever since they were born. When the Hudson and Dunbar families were merged due to the marriage of Patrick's father and Brody's mother, the emotional bond between them went even further now that they were not only each other's best friend but family as well, and even though they weren't related by blood, it surely felt that way. They have been living together ever since the marriage of their respective parents.
Over the years, their relationship has developed certain characteristics that makes their relationship unique to that of others. Some of them may look or sound weird to others, but neither of them care about their opinions at all.