Learn the appropriate times for swearing. Having a filthy mouth is not a badge of honor. But let's face it, in today's culture everyone curses. When I am around a certain group of friends we swear more than a group of drunken bikers. But any other time I chose my words very cautiously. I know whom it is appropriate to curse in front of and who it's not. It's never appropriate to curse in public, around children or the elderly, at work, school, church, funerals, weddings. So only use swear words in the privacy of your home, or the home of other fowl mouthed people.
Tip your waitress. A good friend of mine that I've known since childhood, never tips her waitress. After many embarrassing lunch dates, I asked why she didn't tip. She said growing up her parents never tipped so she didn't know when she was supposed to. Any time you go to an actual sit down restaurant(not fast food) you should tip. It's also very nice to tip your hair dresser and the person who does your nails. After all, these people are very under paid.
Learn where your personal space is, and stay out of others. There is not many situations more uncomfortable than standing in line at the supermarket or target and the person behind you standing right behind you. Most of the time you can feel their breathe on you. Or having someone talk to you and them be an inch from your face. If you have never had this to happen to you, then you are probably the one doing it to others. Rule of thumb, stay at the very least an arms length away from others.
Don't chew gum, ever. This is my biggest pet peeve ever. I despise gum chewing with a passion. It is very gross, unsanitary and it makes you look like a cow chewing grass. The noise of someone chewing gum is worse than nails on a chalkboard. Okay, so now i'm just ranting. But seriously, it is one of the most ill mannered things you can do. And to all gum chewers of the world, just spit it out, for the sake of the rest of us.