Don't worry I'll include a "favorite things about southern california" list later. I'll just need a LOT more time to think about it.
1. Too much sun - Any of the infamous leathery-skinned cougars that occupy the region would tell you that the sun is the best thing about Southern California, as would any one who has some sort of seasonal depression disorder. However, my skin is healthy and the rain makes me happy. I'm not even asking for flash-flooding (which can be just as annoying as too much sunshine) I'd just like to see a little bit more contrast in the weather. The sun can't be beautiful every day, you need the rain to remind you that it's beautiful.
2. Congestion - I would say traffic, but to be honest, it really doesn't bother me as much as it does some people. However, I do find myself being annoyed by it at sometimes, so I'll include it in a broader category: Congestion. Being from Houston, I'm used to being able to drive about 15 minutes to open spaces (fields, trees, nature in general). This is something I wish I would have taken more advantage of when I lived there. Since everyone and their mother wants to live in Southern California, such luxuries cannot be afforded around here. Even if you don't utilize these luxuries, it's nice to know that you can go somewhere else at a reasonably close distance besides your room when you just want to get away from people.
3. Douche bags - There is an alarming amount of douche-bagery committed in this region. Don't get me wrong, there are plenty of douche-bags in Texas, but this area is saturated with them. Most californians refer to them as "bros" rather than douche-bags, but don't let the name fool you, they're douche-bags. Here are the characteristics that make up what a southern california douche-bag or "bro" is: 1) Crippling insecurities which lead to a need for validation in all the aspects of life that don't matter (clothing, automobile, the appearance of being tough), 2) Huge biceps and skinny legs (countless hours spent on sculpting the money muscles and ignoring all others. In other words, if you find yourself having to fight one, kick 'em in the knees.), 3) a strong belief in their innate ability to compete in the Ultimate Fighting Championships, and 4) a tendency to act like an idiot, regardless of their actual IQ (although I would imagine it's usually pretty low).
Of course I'm missing some popular ones (rude people, USC football fans, pollution, soap-boxery, the lakers, name-dropping etc.) but these are my three least favorite things about Southern California.