Pain and embarrassment.
Again, each of us can believe whatever we choose regarding how set up Tourette's Guy is. If you want to believe that Danny was just a tremendously gifted actor with an amazing stage presence, fine. If you prefer to believe that there was a magical invisible floating video camera that flew around Danny's house every day and secreted away to YouTube headquarters every night, go for it. We don't really know, and it's only important in the sense that it might impact our level of enjoyment, so we should each feel free to interpret it however we want.
That said, Danny was a showman of the finest caliber.
The first clip below never fails to make me laugh. He couldn't set himself up for a pratfall any more deliberately. It's genius slapstick performed with hilariously obvious execution. He yells at his son for having the gall to walk in the front door, but I don't think it's done in anger. Actually, this might sound ridiculous, but I think he's rarely angry in the true sense. He could be happy, amazed, contemplative, embarrassed or pissed off, but it will always sound to us like pissed off.
He was fine with being the way he was, but that doesn't mean he was never embarrassed. When his supporting cast laughed at him or when he did something stupid, he was shamed into yelling profanities or the occasional "Bob Saget." And I think he earned the right to express it however he wanted to. If our least flattering moments were broadcast to a massive gaggle of adolescents and twentysomethings, we'd have all moral right to make an obscenity of any 80s/90s television sitcom father we saw fit. It's really too bad Bob Saget's already taken, because the way Danny said it, he had no business saying it around children.