I Appreciate Honesty

How do you know when you're being too honest to someone to the point that you might come across as harsh? People often say they appreciate my honesty, but as soon as I say something they don't like while being honest they completely change their tune. I'm a very blunt and to the point person who is absolutely horrible at lying(I'll start grinning and hesitating on my words whenever I try to be dishonest in anyway). Because of that I'm not the type that can or will sugarcoat things. I'm so brutally honest, which causes problems because I don't know the line between being honest and being too honest.