Direct alternatives:
* Not really.
* I'm not sure.
* I'd rather not.
* I can't.
* I won't.
* Unfortunately, no.
More polite alternatives:
* I appreciate the offer, but I'm not able to do that.
* Thank you, but I'm not interested.
* That's a nice idea, but I'm going to pass.
* I'm already committed to something else.
* Perhaps another time.
* I'm not the right person for that.
Gentle alternatives:
* Let me think about that.
* Maybe, but I'll need to get back to you.
* I'll have to see what my schedule looks like.
Humorous alternatives (use with caution!):
* My mother told me not to talk to strangers.
* My dog ate my homework (or, in this case, my agreement).
* I'm allergic to that.
Remember:
* The best alternative depends on the situation and your relationship with the person.
* Be respectful and polite even when declining.
* Offer an alternative if possible, even if it's just a simple "thanks for asking."
By using a variety of alternatives to "no," you can express your refusal clearly while maintaining a positive and respectful tone.