לזכות ידי"נ הרב משה גבריאל בן יהודית לברכה והצלחה בכל מעשי ידיו!
The Chofetz Chaim writes [4/12] that if one speaks lashon hara and his words are accepted by the listeners then he must do teshuva as for an aveira bein adam la-chaveiro but if his words aren't accepted then he must do teshuva as for an aveira bein adam la-makom.
It emerges from his words that one is only guilty of an infraction of bein adam la-chaveiro when he harms his friend in some way – monetarily, his honor or otherwise. But, as they say on the basketball courts, "no harm, no foul" [I used to play in a rough neighborhood where the rule was "no death, no foul"], at least on a bein adam la-chaveiro level.
Rav Hunter asserted that this is not correct. When one acts against his friend it is a breach of bein adam la-chaveiro regardless of the outcome.
There is a proof for this assertion: The Chinuch cites the Rambam as saying that when one curses his friend it doesn't harm him but is forbidden anyway. Yet the Rambam paskens that when one curses his friend he must ask forgiveness from him. So we see that even when not causing actual harm but just acting in opposition to his friend is enough to qualify as a breach in Bein Adam La-chaveiro.
[ספר זכרון עמ' שלה-שלו. ועי' בס' ביאורים ועיונים על ב"מ עמ' רמ"א-רמ"ב שניסה ליישב את דברי הח"ח].