Thanks for the invitation, but ...
I'll have to pass this time.
No, I can't do you a favour.
Could we do it another time?
I wish I had more time.
Let me think about it.
Mmm, I don't really like karaoke.
You know I'd love to, but I can't.
I can't. I'm so sorry!
I don't think I have time.
My schedule is completly full.
Maybe later on when I have more time.
I just want to go home. Sorry.
Let's take a rain check.
My apologies, but it's not possible.
I appreciate the offer, but ...
No way
I don't think it will work, I'm sorry.
I'm afraid I can't right now.
Sorry, I'm going to the gym.