I'm cool off that - You're not interested in any of the good stuff. It could be

You're not interested in any of the good stuff. It could be drugs, food, drinks, or anything you can pass around and take a hit of.

I'm cool off that, I just had a whole pizza and I'm still full.

I'm cool off that, I just took a hit and I'm still high.

I'm cool off that, I just drank a whole soda and I'm still wasted.