Honesty is being truthful. Blunt is getting straight to the point without dressing anything up. The difference is the person/s patience levels according to the circumstances! A person can be truthful without being harsh ie in a tactful polite way. A person is blunt through lack of tolerance for that person, situation, experience etc. I hope you get what I mean!
Most people are just rude. I wish people would just shut up most of the time. When I'm asked for my opinion I'll answer honestly, but that doesn't mean I have to be rude. I hate when people hide behind the silly excuse of being honest.