Similar to the phrase "corn-fed" which describes one who attaches to Southern styles and ideals. One who is porn-fed grew up with pornographic devices, especially internet porn and is addicted to them.
Jen: "Alex won't come out of his room! I think I can hear the faint 'uhn's' and 'ah's' of his porn.
Josh: "He was addicted to that stuff before he could even ejaculate. Don't be surprised"
Jen: "Porn-fed bastard"