“Love means never having to say you’re sorry” (Erich Segal). Despite the religion of the author, this quotation does not represent a traditional Jewish view of life.
Following certain guidelines Judaism teaches us that if we love our fellow man, we will admonish him and to attempt to improve his behavior if we see him stray. “Do not hate your brother in your heart, you shall reprove your friend…” (Lev. 19:17). One who is motivated by love, and not by hatred, is taught to take action in the face of wrongdoing.
In the “restaurant case” you describe in your question I honestly can’t know if the person who spoke to you did so out of love for you and wanting only good for you, or if he did it for some personal ulterior motive. I would like to think that he did it for a positive reason.
The effectiveness of words of admonition is usually directly related to the sincerity of the person doing the rebuking and his love for the person being admonished. “Words that come from the heart enter the heart.”
People can sense if rebuke is motivated by love, anger, or righteous indignation, and it will only be effective if love is the principle factor behind it.
An esteemed Torah scholar once entered a taxi (in Israel). The taxi driver was about to turn the key in the ignition, when the rabbi put his hand on the driver’s hand and asked him, “Do you work on Shabbat?”
The driver looked into the rabbi’s eyes and felt incapable of admitting that he transgressed Shabbat. On the other hand, being an honest person, the driver could not deny the truth. The driver immediately took an oath in his heart never again to drive on Shabbat, and turned to the rabbi and said, “No I do not work on Shabbat.”
The rabbi smiled and replied, “Good, let’s go.”
From that time one, the taxi driver and his family made a commitment to observe Shabbat. Of course, the taxi driver would probably have responded quite differently to anyone else, and the rabbi would not necessarily have made this inquiry of any taxi driver. However, the effectiveness of the “rebuke” was due to the spirit in which the words were said.