Dear Sir or Madam:
You occupy a particularly critical - and fortunate - place in the flow of traffic, as the people lined up behind you cannot move until you do. For this reason it is not a good idea to screw around with your cell phone, apply makeup, or read the newspaper while you wait for the left turn signal to light. This causes the people behind you to get stuck at the light that you invariably end up noticing with just enough time to let one car - yours - through the intersection.
People like me get aggravated when you zone out and fail to pay attention to the signal, causing us to sit in traffic for an annoying amount of wasted time. In addition, there is a certain bad karma associated with screwing over your fellow motorists in this way, and I suspect that your inconsiderate behavior might come back to haunt you.
Oh - and may a louse and a thousand of her hungriest offspring permanently infest your nether regions.