Use "don't" instead of "can't". Works wonders, trust me. There was actually an article on Lifehacker regarding this. "Sorry, I don't do x." Doesn't fit all si

Use "don't" instead of "can't". Works wonders, trust me. There was actually an article on Lifehacker regarding this. "Sorry, I don't do x." Doesn't fit all situations, but for a lot of invitations it works wonders: restaurants/movies/concerts/meetings etc. You can get creative: "I don't do x with friends" if it's a business project. :-)