Here are two instances that I found where Jason Voorhees has his penis mentioned in regards to its large size. The first gif is from Jason X where a man says "he's a big boy" and the woman he is speaking to responds "I bet he's hung like a mammoth".
The second is a clip from Freddy vs Jason where one woman taunts Freddy by saying his "butter knives" are small and that he's compensating for something small between his legs, while she then follows with "Jason has got this big ole thing".
So slasher fuckers start with Jason for a reason, and we always keep coming back for more. He's our collective number one murder husband.