LOLcow qualities:
1. Very eccentric behavior and opinions. Examples: Chris's sweetheart search, ADF's queermunism, the Loveshys' assumption that the government should provide them with women.
2. Trollability. Not a must but a big contributing lolcowy factor. The easier a person's berserk buttons can be pushed, the more lulz.
3. Creepy sexual behavior or fetishes. Examples: Again, Chris's retarded girlfriend attraction methods and - later - tomgirl shit. JustinRPG's pokemon scat fetish. Pamperchu... I don't think I need to say more.
4. Weird dress style, incorporation of fandoms or idiosyncrasies into clothing. Examples: Chris's medallions, Anthos's Autobot pirate costume (the latter is actually sorta cool IMO), ADF's uniforms.
5. Infantile character traits: Living at home, not having a regular income, being completely dependent on parents. Examples: Chris's holing up in his room in Casa Chandler, Pamperchu's voluntary decision to live like a baby.
6. Exhibitionism, especially online exhibitionism: Being completely open about one's sexual life and preferences, talking about them at length on the internet, revealing embarrassing personal details on the web, doxing oneself. This facilitates trolling (see point #2) and exposes point 3. for all the world to see. Pamperchu's diaper fetish could be seen as a weird, yet legitimate sexual kink if he DIDN'T FUCKING TALK ABOUT IT IN HIS VIDEOS FOR THE ENTIRE UNIVERSE TO WATCH.
7. Narcissism, unwarranted self importance. This is what drives points #6, #4, #2 and, to an extent, #1. Thinking him- or herself as a genius, the LOLcow expects endless praise from the world for stuff that is actually very trite and retarded. Examples: Chris's Sonichu comic, Gloria's Maradonia crap, Anthos's anti-trolling vigilante act.
Note that lack of intelligence is not among these points. Some LOLcows may actually have a high IQ - good raw intelligence, but they are nonetheless completely retarded in the field of social interaction or managing their everyday life. So the difference between a LOLcow and an idiot is simply that the idiot is boring, the LOLcow is entertaining because of the strange crap he or she will do and put up on the internet for everyone to take part in.