Depression can be a very dangerous thing for a person to go through and sometimes trying to put on a good face feels impossible. You should always try to avoid having a negative attitude towards others, especially if they never deserved it. Don't take out your depression on other people. I wouldn't go as far as to say you have to be extremely pleasant to others but, at the very least, keep to yourself for the time you're feeling down and if you have to interact with anyone, keep it short and keep it positive.
Talking to people who are close to you can help if they're open to listening. Going online to share your feelings or issues can help too if the former isn't possible.