The phrase is a play off "pervert" and "to wank." Literally, means someone who masturbates with perverted qualities. It is often used in a playful sense to label someone who is not shy about hiding his sexual appetite.

Can also be used negatively to label someone as a chronic masturbater or someone with immoral sexual desires; however, it is more often used in a playful sense.

a great name to confuse someone who is annoying you!
they have no clue what it is, and well, you get a great laugh at them wanting to know what it is! and when they ask just tell them that they are pervy wanker!! :D