For me, it is when they make guys look like freaking chicks and I can never tell which one they are. This goes for Haku from Naruto and some guy from Sengoku Basara whose name I forgot.
EDIT: Also, chicks with extremely oversized breasts.
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When the characters are hot but you're unsure of their age so you don't know whether you should feel dirty or not for being attracted to them.