I agree, poor Jack who tries so hard to be the very best father/husband for all of them at all times. If there's any one thing this show teaches us, it's that everything that happens to you as a child colors your whole future -- and that means parents have to be perfect every second of every day and that's just impossible.
I was once a young hippy-type mother, open and encouraging to all things original and creative, and yet my son has a memory of the two of us walking up to a Dairy Queen when he was about four: He said he wanted green ice cream and according to him I said, "They don't have green ice cream here," in a tone of voice that made him feel stupid. I don't know if I was, tired, distracted, or just a down right terrible mother, but there it is. He remembered it forever. You can't win.
Little Kevin popping up and scaring his dad was the cutest moment ever.