I have personally noticed that if a person is accused of speaking Lashon Hara, they have a strong tendency to get very defensive.
This seems to me to be something that is above and beyond the standard defensiveness that people respond when when generally accused of wrong doing.
Have I spotted something real? Are there any sources that also point this out and perhaps offer a reason, as well as advice on how to get people to stop talking Lashon Hara in a way that will have more success?
The reason why I suspect there might be an answer is because a Rosh Yeshiva once told me that the reason we speak Lashon Hara is actually not so much to do with the yeitzer hara, although this was a long time ago, I don't remember his full explanation or if he gave any sources, but I do believe there is something unique about this one particular aveira.