Based on my life experiences, one thing I've learned is that even though it's all right to be angry, it's how you handle the anger that makes a difference. For example, if you happen to send a text message to a friend and they don't respond back, you might feel like they're completely ignoring you. While that's perfectly understandable, there's a healthy way to approach this.
For example, you could send them a message a few days later asking if they received the message. As another example, you could approach them in person and ask.
However, there's also an unhealthy way to handle this, which would include jumping to conclusions, insulting them, or sending a very rude text message back. If it's not handled correctly, anger can be destructive, and may even ruin friendships.