Hate to say this, but Kevin could definitely be a jerk at times, especially when he's in high school. While Kevin and Randall's arguments steal the show in the first season, his tiffs with Jack and Rebecca take the cake in the second. You know what that means? There are probably a number of things he wish he didn't say to his dad.
Most recently, we saw that he got into it with his parents about having to go to community college after tearing his ACL playing football. And moments before that, he tells his dad that "no one cares" about the entertainment center he's building. You can see this really stings Jack, particularly because Jack mentioned how much Kevin used to like building things when he was a little kid. Although Kevin realizes the error in his ways and calls his mom to apologize about his outburst, our hearts ache knowing Jack never gets the apology he asked for in his note.
And how can we forget the scene with the amendments? After making his rounds to Sophie and Randall to apologize, Kevin breaks down after turning his list over and reading the word "Dad." This is particularly haunting if you think back to the fight Kevin has with his dad after the Pitt football coach leaves their house, when Kevin tells Jack he "knows the feeling" of being embarrassed well, trying to take a dig at his dad's alcoholism. Unfortunately for present-day Kevin, the tables have turned when it comes to substance abuse.
Kevin knows he was in the wrong, but struggles with the fact he was too late to say sorry.