judging people

I'm pretty bad at judging people. Sometimes I can't recognize sarcasm. Sometimes I can't tell when someone is being a jerk. Sometimes I seem to get a long with someone who I hear from other people that this person is real bastard. I have also been led on by girls before and thats kind of annoying. People say it is bad to judge, but I believe to some degree it is useful to be able to tell what someone really means or their true intentions after properly judging them from what they say and how they act. Its like I talk to a person and I try to get an impression from them and I am like ok ok I think this is what is going on with them, then I go to someone I trust, talk to them, and they tell me "dude your wrong". I need people to be more straight forward I guess. When I try to follow my feelings to get that "impression" I am told by a good friend of mine that I am being "mellow dramatic". w/e IDK.............brough