How would you turn down a petition you disagreed with?

I'm not talking about a right-wing petition. That would be very easy. I'm talking about a situation where you disagree with a person or group that you normally agree with. Luckily, that hasn't happened to me, but it would really feel awkward if it did! No two people agree on every issue, so this could be possible for anybody. Has this happened to anybody here? How did you handle it?

"No thanks, that's not really a priority for me"

or

"No, sorry, I can't support that issue framed in that manner, but I'll certainly give it some more thought"

The guy had two petitions. After he explained them to me, I told him I'd sign the first but not the second. As I was signing, he asked why I wasn't interested in signing the second and I told him. After I explained my posion, he said he'd never thought about it that way before.

It was all very polite.

At this point in time I have yet to decide on the subject matter at hand. And than I would ask them for a way to contact them later.

...usually does the trick.

"I'd need more time to look that one over before I could sign it."
"I'm really not comfortable with the way that's written. It's too broad/narrow/dense/facistic/republican/vauge/whatever."
"I'm not convinved this is a spending priority right now."
"I think this should be handled at some other level. It really isn't appropriate for the state."

I've got a lot of practice at this, I live in what has got to be the petition circulating capitol of the universe. I don't mind petitions (I'm all for civic involvement) but when I'm headed into the grocery store with a four year old hanging off me like a leech, it's not the best time to stop, read and sign a petition for ferret legalization or whatever the heck is on the clipboard this week.