The tendency for male internet
denizens to, in short, suck up to and give a lot of attention to females on the internet. This raises their chances of ever getting laid with said females by about 0.0%.
Symptoms of girl on the internet syndrome include making a big fuss when a person is found to be female, complimenting her every time she posts a picture, regarding her as a quality poster in a forum even if she isn't, giving her mindless attention, denying having girl on the internet syndrome, making sexist jokes so as to "prove" no preference toward internet females, annoying women, asking women to be e-girlfriends, alienating women, asking for nude pics, and wondering why women don't seem to be on the internet that much.
Person 1: OMG, a girl on the Internet! I better respond every time she posts a pic of herself by saying she looks pretty. Maybe I'll get into her pants!
Person 2: dude, you have girl on the internet syndrome.
Person 1: no I don't! Women belong in the kitchen.
Person 2: uhh, OK.