When driving a vehicle and there's other vehicles around you, if you want to make a turn, or make a lane change, please use your freaking turn signal!
Other drivers (like me) need to know that you intend to make a turn, right or left, so we can safely accommodate you, and not smash into your ass. Whenever you are going to make a turn, let other drivers (behind and in front of you) know, by using your turn signal. I am not a mind reader, I don't know that you are about to make a turn unless you let me know.
You are piloting a potentially deadly 4,000 pound vehicle. Please let everyone know what you intend to do with it. Be smart - use your turn signal! Unless you prefer that we smash into you.
In traffic, making a turn without using your turn signal is downright dangerous. Using your turn signal is common safety. And common courtesy. And common sense. Use it! Make it a habit.