It stands for '3D Pig Disgusting'. It's when a guy who likes anime prefers a 2 dimensional drawing of an anime girl over 3 dimensional actual real live women. I hadn't heard of the concept until today. Apparently the phrase came from some Korean guy's rant on video. :P
Well, I'm not a boy anymore, but I was very likely stupid when I was that age. XD Not anymore. Far more interested in the ladies than any mass entertainment. :D
Well the "men" ( as they like to call themselves) in my class do this ( in the quotation marks) "*fart/burp noises* I'M A BANANA!!!!!!!!!' SHUT UP B4 I FART ON YOU!!!!!!!!' I'M A TURTLE!!!!!"
I think the girls themselves are cosplaying anime characters but the boys prefer to look at the two-dimensional characters on-screen. It's the 3DPD effect I told Masqurade about on here. I think their lesbianism is besides the point. Most guys I know would be ogling the girls kissing. ;)