Number Four is, well, very smart. He also was the target of most of our teasing before Number Six came along. Peter tended to be slightly smaller and less athletic than the rest of us - even Number Five. And he was a little, well, book & tech smart.
All of that adds up to one thing:

Oh, it's not nice, to be sure. I can see that now...some 30 years later. And although he is still slightly less athletic than most of the Brothers, he is no longer slightly smaller than most of them. Besides, we have all matured to a point where there is no senseless teasing amongst or targeted at any one of us.
Mom & Dad, please get up off the floor and stop laughing.
Hey, he's a really good uncle to my children. He plays with them and entertains them - most of the time in an age-appropriate manner. Today, he's spending several hours playing Mario Kart with them (their birthday present to him). He even stays relatively patient with them, if he's not in a liquid-waste-poor mood. A bonus - if we avoid the subject of illegal immigration, we can have decent conversations.
These are the things that tend to be more and more important to me. True, he's not married and is not terribly active in the Church right now, but he's only 30-something. He should have another 50-plus years to figure those things out.
In the words of the all-wise Neil Diamond, "He ain't feckless, he's my brother."
I love you, Pete.