In The Name of Allah, The Most Merciful, The Bestower of Mercy.

Asma Bint Yazid, may Allah be pleased with her, said: The Prophet, peace and blessings of Allah be upon him, said, “Shall I not tell you about the best of you?” They said, “Certainly”. The Prophet said, “Those who, if they are seen, they remind you of Allah. Shall I not tell you about the worst of you?” They said, “Certainly”. The Prophet said, “Those who carry tales and ruin relations between those who loved one another, seeking misery for the innocent.” [1]

“Those who carry tales”. 

Their habit – constantly and always – is to embark upon transmitting corrupt speech.

They do this to sow corruption (or ruin the good relationships between people).

You find two people – two people upon brotherhood and friendship, however due to the endevour of a tale-carrier, he (the tale-carrier) does not cease transmitting speech from this one to that one until an incident occurs between them…[2] [End of quote]

One of the bad behaviours of some people during our teenager years was that they would feign agreement to gain your trust and then transmit your disagreements to someone else whom they knew strongly disagrees with you. This was nothing but treachery regardless of the good character put on by the perpetrator.

[1] al-Adab al-Mufrad 323
[2] https://www.alathar.net/home/esound/index.php?op=codevi&coid=258598 a paraphrased excerpt from a statement of Imam Al-Albani, may Allah have mercy upon him.