Some people apparently think it's funny and original to coin a new noun and call someone "such a new noun". To those people: it's usually not funny, and it's certainly not original.
Taken from actual Urban Dictionary definitions:
"Kirsten is such a hypochristian."
"Stevie is such a slutbag!"
"He's such a nintendrone."
"He's such a wimpy nucker!"
"That prude is such a Mar!"
"hahahaha ur such a Davis"
"Oh B, you are such a narutard."
"Yeah, he's such a masnun."
"He's such a vidiot."
"Look at Jeff, he's such a lurp!"
"Allison is such a skanksta."
"Your girlfriend is such a mise!"
"God, stop being such a natch."
"Jkea, you are such a nerb."
"She is such a facehead!"
"Yazzy, you're such a snigger."
"You're such a foge!"
"She's such a skemo."
Another banal convention popular on UD: "pulling a (name)", where one inserts any name of their choice.