Generally, I like Apple products. But some of their stuff is just the worst. Here's my list of stuff I've used that I really dislike.
Ranked from worst to less-worse.
iMessage: sending a text message should be quick; really quick. You should click Send and it should be sent. There are days where messages will take 1-2 minutes to send. For a product I use hundreds of times a week, this is downright painful.
iPhoto: storing image files in a single Library file is a terrible idea. The Library package makes it difficult to access originals (to do so you need to find the Library file, right-click and select “Show Package Contents”), and can easily become corrupt. iPhoto itself is bloated, and annoyingly slow to use. For me, the best way to organize photos is place the actual image files in old-fashioned folders (date stamped with the year: 2013, 2012, etc...)
Magic Mouse: Bluetooth has always been finicky with me. On every machine: old iMac, new iMac, Macbook Pro, Macbook Air it's consistently flakey. This is most pronounced with the Magic Mouse. There are times where the mouse simply won't pair, and it takes repeated steps of turning it off, rebooting, etc... to get it to pair successfully.
Airport Express: don't buy it. If you do, you'll be constantly turning it off and on again in order to restore WiFi connectivity.
Numbers: spreadsheets is one domain where Microsoft wins. Every time I've used it, or spoken with others that have to use it, I'm struck by how much you can't do. Functions I use all the time (like Save as CSV and Text-to-Columns) are difficult in Numbers. Also: I've had customers tell me that large datasets are practically impossible to work with in Numbers.
Those are my six. What did I miss?