Sefer Chofetz Chaim Perek 2, Halacha 2, Note 2

The answer to Tosfos’ view on apei tlasa is that straight out negative lashon hara is forbidden to be said whether in front of 3 or more people or even to the antagonist’s straight up lashon hara is forbidden, also to listen and accept as true. However the leniency is in a case where the statement could be taken in two ways, positive or negative. The key to the leniency is if you don’t feel embarrassed at all to be willing to say it to his face then you may say it to him or her or even in front of 3 people since it will definitely get back to the person being talked about. However if you feel any embarrassment to say it or if your expressions, voice, physical, etc is of a negative connotation it should not be said.