That's from comic 50 and the quote is "Nale! Stop hitting your twin brother in his soft undeveloped baby skull!" Sadly it doesn't help the "debate" in either direction.
Dang, I thought that I had something. Oh well.
Awesome avatar by Cuthalion
Spoiler: Old Avatars
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By Ceika, Ceika, Linklel (Except for one that appears to be lost to time)