You should know better. Many people don't.
Do not touch the screen. If you have a flat panel monitor, and most people do now, then you may be in the habit of touching the screen, particularly when showing someone something. If you touch the screen, you leave oils on it that you'll be tempted to clean with something that will leave tiny scratches on the screen, plus you'll do slight damage to the liquid crystals that make it work. Many people touch the screen all the time and don't see any harm so they are clueless why it stops working right later. This is a little like leaving oil in the car for fifty thousand miles, the damage is minimal at first but as time goes on it accumulates until you have an expensive smoking ruin.
Do not forward without research. I cannot tell you how many times I have received an email that tells me something interesting only to discover that it was a lie. Not only am I lied to, usually by someone I trust, I also see that dozens of other people were sent the same lie. I find being lied to offensive even if the person who sent it didn't know better. They should have. All it usually takes is a quick search on snopes.com to find out that the most interesting or scary emails are hoaxes. I try to be calm and rational. I think I am more successful than I used to be. I will now reply to the sender and let them know that they have passed on a lie to me. I try to avoid pointing out that it is what the "bear false witness" commandment is about. I resist the urge to email every friend they sent it to and every friend that got it in the list up to them letting them know that someone they should be able to trust is spreading lies. I try to avoid that... at least the first time. (This doesn't mean you shouldn't forward funny, clever or interesting things, just make sure that they are not lies.)
For those of you new to email, here are some things that are commonly lied about:
Do not call this "/" a back-slash. The "/" character is a slash or a forward-slash. It is not a back-slash. This "\" is a back slash. The two slashes look similar but the one leaning from lower left to upper right is used in Unix, Linux and Mac specifically to denote directories. The back-slash is used in DOS and decent systems to denote directories. The World Wide Web was built on Unix and even Windows servers provide web pages with forward slashes, never back-slashes. I've heard radio and news commentators make this mistake, and it is always a mistake. It makes you sound like you have never noticed that every web page (ever) uses the same kind of slash.