I'm a nice guy. 90% of the time, I'm a pretty good person. But I have a few observations to make.
People who obsess over sports teams, clothing, or anything else: don't make fun of nerds. Ever. Because an obsession with Burberry or Prada or the Dallas Cowboys is no different from an obsession with D&D, Star Wars, or video games. You're a fanboy, too. So don't mock someone for a different obsession. Everyone has one. Learn to deal with it.
There's no such thing as a "smart person who just made some bad decisions." Everyone makes bad decisions. But smart people don't let those bad decisions define themselves. Someone who justifies their life as the product of a few bad decisions isn't smart. They're delusional.
Don't try to be more than you are. Some people are smart. Some people are poets. Some people are athletes. Just because you can, say, jot a few lines when the mood hits you, does not make you a writer. No more than hanging out in the pool makes you a swimmer. Suck it up. Be good at your own thing and deal with it.
Don't tell the government to get out of Main Street and leave the governing to the people, and then turn around and beg for no abortions, stricter immigration laws, and general regulation of everything that opposes your personal moral code. There is a middle ground. This is not it.
Stop reading literature and assuming it'll make you look smart. Just because you list Hemingway on your "favorite books" section of your Facebook profile doesn't mean you're intelligent. It just looks like you're begging for attention.
While we're on the topic of pretentiousness: the same as above goes for movies, too. Just because you know who Ingmar Bergman is does not make you a film buff.
Respect other people's religions. With the exception of Scientology, just about every religion out there deserves respect, whether you think they're right or wrong. Don't be a jerk. Respect atheists, too, if you aren't one.Just give everyone their due respect.
And finally, just don't be more moronic than you were born. Not everyone is a genius. But you shouldn't feel the need to prove that all over the place.