Okay, America. I am putting you on notice. If you don't stop the following annoying things, I may have to take away your after-dinner cookie privileges.
Ringtones
We've talked about this before, but it bears mentioning again. I really don't care to hear your favorite song, or mine, for that matter, as your ringtone. It is most annoying. Your cell phone is a PHONE. It should ring...quietly. Vibrate is even better. Anything else is just noise pollution.
Turn Signal
There is a lever located on the left side of your steering wheel inside of your car (I know...shocking, isn't it?). When you push this lever up, towards the sky, it turns on a blinking light located externally on the right side of your car, both front and rear, that notifies other drivers that your are turning right. When you push it down, towards the ground, it notifies other drivers that you are turning left by enabling a blinking light similar to the one mentioned above, but located on the left side of the car. when you push it back to its center position, it turns off all blinking lights and other drivers will assume that you are continuing forward without turning. Not only is it good manners to use this fun and informative feature, it is required by law in all fifty states. PLEASE USE IT. Thank you.
Your Car Stereo
This one's easy...TURN IT DOWN. I don't want to hear your garbled music and all of your sheet metal vibrating in your 1983 Corolla. Better yet, save the money you would have spent on the subwoofer and amp at Best Buy and, instead, take a college course, or put it towards music lessons, or feed the hungry. You'll feel better, and so will I.
Common Courtesy
Please, if you are sitting in front of someone tall on an airplane, don't put your seat back. It makes an already uncomfortable position even worse. And, if you do, don't be shocked when you feel our knees in your lower spine. It's not because we want to push against your seat, its because you have given us tall folks no other option. We are all stuck on this plane together...let's be nice to each other, m'kay?
Blue Tooth Headsets
Unless you are actively engaged in a conversation, take it off. You look ridiculous. And, you don't have to yell. I really don't want to know about your battle with foot fungus, or your love life, or what you need to bring home for dinner.
Speaking of cell phones...
It is just plain RUDE to call someone and talk to them while you should be engaged in doing something else, like paying for your groceries. Talk to the REAL people that exist in your physical space that you are interacting with. It will not kill you to call that person back after you get finished with your current task. You aren't that important...trust me, I know. The only reason to take the call is if you are a doctor and lives are at stake.
Smile
This is really simple, and will go a long way towards making your day better. When you encounter other people, smile. It is pleasant, and in times of need, people are more likely to help you if you are kind and friendly. It isn't hard to do this. At least, it's no harder to do this than it is to scowl at the rest of the world. This helps even if you are having a bad day. If you smile at people, they will smile back. Try it...it really does work. Unless you're initials are TL and you live in Wisconsin...you scare people when you smile (just kidding, T. You know I love you, man).
Buy Clothes That Fit
Guys...I really don't care if you are wearing boxers or briefs, so you don't need to show them to me. The waist size on the tag should closely match the circumference of your actual waist. They should fit comfortably, and if they are slightly too large, then use a belt. Girls, shirts and pants that are two sizes too small are NOT attractive. I know you have it tough, what with society telling you that 'abnormally thin=pretty'. Believe it or not, most people don't agree with that. If you wear clothes that fit, it is more flattering, which actually increases your attractiveness. Also, the shirt should cover the waist completely, even if you have to bend over to pick up a dropped object. I will not elaborate further, since I am striving to be gentlemanly.
Okay...follow these simple guidelines and your life will be enriched. And, more importantly, so will mine. 
Enough snarkiness...back to work. Oh, and feel free to add your own grievances in the comments.