Rule #6: You can only reject a challange you were given ONLY IF it breaks your rules, or if it "Does not fit your difficulty", or if it is one of those downright stupid challanges that nobody would even consider doing, but yeah. If you get a challange you want to reject but you didn't say no to, too bad. You have to put up with it.
Not to be rude, but it does say that on page 1. Obviously it's ultimately up to you, but remember that you did ask the community.