Halacha 1: There are 3 levels of lashon hara all worse than the next.
A. Saying lashon hara behind one’s back which not only do you get a sin of lashon hara but you also get a curse for hurting someone in a hidden way.
B. Saying lashon hara about someone in the crowd. So he is there but it is not to his face.
C. Saying lashon hara to one’s face with a group around which not only do you have the sins of lashon hara and ona’as devarim which is insulting someone to his or her face but you are also acting in a very negative manner by using the terrible attribute of audacity and chutzpah besides the fact that you embarrassed the guy which if done without teshuva one has no share in the World to Come.
Halacha 2: There is a chaza”l that says if one is willing to say something to the guy’s face then it must be permissible to say but that is only in context of avak lashon hara, a statement that can be taken in two ways, good or bad, depending on one’s connotations, voice, movements, who it’s being said to etc. The fact that one is willing to say it to the guy’s face is usually a litmus test that he is saying something positive because the nature of a person is to avoid someone he is speaking bad about but that does not mean that if he is willing to speak negatively about the guy to his face it is permissible. It just means you are willing to stoop so low to go beyond human nature. For example if you say “someone is big” then that can mean he is a big fat lazy shlub or it can mean that he is big and strong and can help people lift things or protect them. Depending on how one says it, does he look or sound nervous when saying it confident. Or is he making gestures that look like he is making fun of the guy. Is it in context of trying to help someone in need or is it with a group of scoffer last that love making fun of people all these things must be taken into account but if he is willing to say the guy is big when he is right there it is most likely an indicator that it’s a positive statement. The key is to think of what you are about to say and how you are going to say it will cause more harm or will help.