Well done.
(,)
Pervert.
(wait. why does the comma even have brackets?)
I believe it's because the titles has different meanings with and without it.
"Well Done, Pervert" is saying "well done" as in "good job" to the pervert. "Well Done Pervert" is using the term "well done" to describe said pervert. "Well done" being a reference to a way to prepare certain foods is, I think, a reference to the term "cooked" which can mean to be in a dangerous or otherwise bad situation.