Simply, a crush on a porn star. Just like having a crush on Brad Pitt, one can have a Porn Crush on any porn star, from Amateur to Professional, from Brent Corrigan to Jenna Jameson.
(The Porn Crush is generally considered non-creepy. Porn Star Obsession is a different thing completely.)
"Man, I've got such a Porn Crush on Jenna Jameson - I have all of her stuff!"
"I would date Chase McKenzie, I have a total Porn Crush on him."