People who run stop signs.

[FishermanTim]

I don't want to change the overall tone of this post, but there's also the contingency of new drivers that take drivers ed classes, where they are only taught how to pass the test.
Not all driver's ed schools are guilty of this, but there seems to be quite a few immigrant drivers that seem to have no clue on how to drive.

I also agree that turn signals are used as often as hemmeroid creme, they're both considered a pain in the a$$.

Now with the ineffective law enforcement, new driving laws (texting & cell phones) that will equally be ignored, and ignorant drivers I'm constantly looking out for #1 when driving, because if I don't I can't rely on the law to!!!!