This is an example of Affirming the Consequent, also known as the Converse Error

Their statement affirms: "if it makes my dick hard, then it's a woman" whereas the assumption being made here is "if it's a woman, then it makes my dick hard". This is the converse of the original statement, and doesn't carry the same logical truth as the original.

It should be noted that the inverse ("if it doesn't make my dick hard, then it isn't a woman") also doesn't, but the contrapositive ("if it's not a woman, it doesn't make my dick hard") does!