I think a lot of people miss the point here. The point and message of the song, is that all this is ironic. By the time he wrote this song, he wasn't sorry for anything he did. In his newer song "Headlights" he explains how sorry he is for this song, and how he "cringes every time he hears on the radio". By the time he wrote "Headlights" he was truly sorry for how he treated his mother, and how he wrote awful songs about her.
The point of this, is that when he wrote this, he hated his "mama", and he wanted to make fun of her, by writing this song.