A person who is constantly looking for attention that he/she can never get in real life. It's also possible that this person has a really crappy life and proceeds to hide it and pretend that he/she's above the people he makes fun of. It is the sole reason why this person constantly screams about his opinion on the internet, looking up videos a bout things he hate and then leaving links to his/her own crappy videos just to get views. This person will also go through great lengths to try and find people that agree with them in hopes of finally getting the sense of belonging somewhere.
An example of an online attention whore would be this guy : alexsavov2 or his alter ego : oldsaviboy
This person is the epitome of attention whores. He constantly goes to every Frozen related posts just to scream that he hates and then proceeds to leave links to his videos about him screaming how he hates Frozen. Sometimes you even see him on videos that have nothing to do with Frozen and then this guy brings it up out of nowhere and then proceeds to scream some more of how much he hates like we get it! Shut up about this damn movie it's been two years! Move on, you're acting no better than the immature Frozen fanboys/fangirls.