Why wouldn't you just wait 'til he comes back and say, "Hey, mind if I borrow your scissors?" - Rogue
Perhaps you don't know when he is coming back and you need to use them for a project that is due very soon. - Spall
If the person has a standard policy of "do not take or use anything from my desk", then yes, you are wrong to violate his will. We're talking about property rights here, and you do not have a right to use his property without his specific or general permission. The same applies whether you are talking about scissors or a house. If a guy working at a store takes the reciepts to the Casino instead of depositing them, but wins, then returns the money in the morning, are you arguing that he did nothing wrong?