To me the biggest defining feature of a lolcow is ego. They not only have to believe they're better then most people but have to be fully committed to it too. They have to think they're so special that they have no choice but to show it off to the world. They have to have no way to look at themselves from others perspectives and see they might be wrong. It takes a special kind of dumb to think like this and it's what makes the best cows to me.
Someone who doesn't fully understand how the internet works. When ever they post something, they automatically think that it's amazing and think everyone will love it. Then as soon as someone disagrees with them or anything negative happens, they'll lose their mind.
They ignore every single piece of advice thrown their way and never learn from mistakes. They also must have an overwhelming desire for attention that keeps them making content despite the constant trolling they face.
i doubt you can even call them lolcows at this point cuz they stop being funny and start being kinda cool but my top favs are always the ones who, despite being weird as balls, are generally very nice and hospitable people and overall just genuine pals that you'd have to be a huge fucking jerk to troll, like ulillillia or wesley willis[do they count if they died before the term lolcow came to fruition?]. runners up are conspiracy theorist francis e dec type dudes whose delusional belief systems are like their own universe in and of themselves and, if adapted into a movie, could quite possibly give they live and total recall a run for their money if done right
The big thing that defines a cow for me is, as previously mentioned, a certain degree of obliviousness. More specifically, a very naive obliviousness. I like cows that are boundlessly optimistic (or better yet, wildly ambitious), who believe that things will get better for them and their ambitions will be fulfilled without any effort or change on their part. This sets them up to fail which is amusing to me in a schadenfreude sort of way, but also kind of makes me want to root for them. The best examples of this are probably classic Chris, ADF, Connor Bible (in a particular part of his cycle), Augustus Sol Invictus, or Derek Savage. Nothing like an underdog.