Casual & Dismissive:
* wtv
* whatevs
* idgaf (I don't give a f***) - this is very informal and should only be used with close friends.
Neutral:
* ok
* k
* sure
Sarcastic:
* sure thing
* whatever you say
* lol ok
It's important to remember that chatspeak is often informal and can be misinterpreted. If you're unsure how someone will interpret your message, it's always best to err on the side of caution and use a more formal way of expressing yourself.