Pho Dang is a word substituted for any expletive of choice. It can be used to describe extreme awesomeness, or extreme terribleness. In genereal, it is a powerful word used to express any sort of powerful emotion.
"Pho dang-it, who stole all of my Halloween candy?!"
"Chuck Norris is a real pho dang."
"That movie last night was pho dang-in' awesome!"