When entering a room, an inconsiderate person will knock and immediately enter. This isn't just rude, it's pointless. The whole point of knocking is to make people aware you're there while you wait for a response! It's not that hard!
One of the things I like to study is old and modern etiquette guidelines! Especially as this sort of thing is dying out - a lot of people have no manners at all! I think a lot of people my age think that being polite makes you boring, and being bitchy makes you characterful or more memorable somehow. Whereas, I think it shows a weakness of character, especially to be rude or unkind!
I'm so bored of being on the computer, but everything I need to get done needs it ;-;