So can you sunder a de-buff cast on yourself and do you have to beat your own CMD to do it or would you just roll against 15+caster level?
Spell Sunder (Su): "Once per rage, the barbarian can attempt to sunder an ongoing spell effect by succeeding at a combat maneuver check. For any effect other than one on a creature, the barbarian must make her combat maneuver check against a CMD of 15 plus the effect's caster level. To sunder an effect on a creature, the barbarian must succeed at a normal sunder combat maneuver against the creature's CMD + 5, ignoring any miss chance caused by a spell or spell-like ability. If successful, the barbarian suppresses the effect for 1 round, or 2 rounds if she exceeded the CMD by 5 to 9. If she exceeds the CMD by 10 or more, the effect is dispelled."
Since you are (presumably) a creature, you would need to succeed at a normal sunder combat maneuver against your CMD + 5.
It doesn't really make much sense, but there you go.