This one receives honourable mention under the "small things" category for me.
CD cases that are of a special, limited edition release which are not a standard size format and do not fit into my current CD storage system. These releases normally come in tin cans or other unwieldy monstrosities. I am a stickler for uniformity when it applies to the appearance of my music collection. My wrath also includes the most horrible, cardboard CD holders.
Be well....