Many years ago, somebody pissed me off. Well, actually he didn't. I think I was more bored than pissed.
So I took one side of his shoes and threw it in the bin on the 7th floor. We were living on the 13th.
I took one, so he would put on one side of the shoe and waste ten minutes or so of his life wondering where the heckaroo is the other side.
I took one, so his head would be muddled as to why on earth a thief would only steal one side of his shoes.
I didn't take both cos it's so lame and boring to have your shoes stolen. Instead, losing just one side of your shoes is more excruciating and frustrating.