やんないじゃない、
できないんだ！（ドヤ！）

ガヴちゃんにピッタリだと思った衝動で描きました、ナナヲアカリさんの曲は良いぞ～！

I don't refuse to do,
I just can't! (Doya!)

I thought it was just like Gabu-chan and with this drive drew it. Nanawo Akari-san's song is great!
堕天使 is fallen [angel], or as 駄 ー poor/worthless. Also 駄目 means "no good; useless; hopeless; etc."