Contraction of Ok, thanks, bye.
Used when you want someone to shut up (you're not exactly trying to be polite,) yet it's not considered as an insult like STFU. Also it can be used when answering a stupid n00b question, or after scolding someone.
I'm not arguing anymore. kthnxbai.
Stop that or I'll ban you. kthnxbai.
^ above isn't as insulting as STFU N00B!
(Pronounced "Kay-Thanks" - One word) Thanking someone for doing something that you aren't really giving them the option to do in the first place. This is always said in a sarcastic tone and there is usually a prolonged emphasis on the "s."
Honey, I know you have the flu, but please go outside and shovel the 7 feet of snow we just got last night. Kthanks.
Signalls the ending of a conversation. Usual follows a distinct point made. k=okay thanx=thankyou bai=goodbye. Kthanxbai replaces the need for "thats the end of it".
Jeremy: Im so much cooler than you.
Andrew: No your not i am much cooler that you idiot.
Jeremy: how rude
Andrew: Just shut up you noob im cooler kthanxbai