A wise woman once didn't give a single fuck about grammar, and invented the word "bestest". It is used to specify if something is the best, among other things.
Nerd1: 0MG LoLz I HaEV C00kies!1
Nerd2: YaY C00KIES!1!111111oneone
Guy trying to look like a cool nerd: YEZ COOKIES ARE TEH BESTEST EVAH LOLOLOLO Nerd1: ...
Nerd1: Asshole.
WARNING: Dont overuse it or you will sound insincere and stupid.
1 (verb) The greatest, awesomest, best thing ever in the world ever! Despite sounding retarded, it is better than saying best.
2 (noun) Word used to describe your favourite person(or people) to have cybersex with. Cybersex is also called "talking" Mostly used in front of small children, parents, other unapproving people.
2 (a converstion)
Person 1: "So, erm, my... bestest... and me, we were "talking" on msn for an hour."
Person 2: "Wow, whats their addy? I need to talk to them!"
Small kid/Parent/Unapproving Person: "Huh?"