Hilchos Lashon Hara, chapter 2, section 10

Also know: the whole permission for a story said in front of three only looks at the speaker. But think about the listener too. If a person knows that the listener will believe the story and perhaps add more bad things to it, it is forbidden to tell such a listener even a hint of something bad about another person, in any case. Telling such a person breaks "Do not place a stumbling block before the blind."

And wherever we said it is forbidden to repeat a story, it is also forbidden to say "I heard this about so-and-so," even without saying who told it first.

With all these details, we can see how much a person should stay away from this permission of "in front of three." In real life, there is almost never a case where all the conditions are met.