Nah kid
What you say when you don't want to do something and you're too lazy to say anything else. It's like you're being a total slacker but you're still being friendly.
Nah kid, I'm not going to the store with you. I'm too lazy.
Nah kid, I'm not helping you with that. I don't want to do anything.
Nah kid, I'm not doing that. I don't want to be bothered.