The Torah says that one is not permitted to plow with an ox and donkey together - לא תחרוש בשור וחמור יחדיו. What is the reason for this prohibition. A number of commentaries say that the reason is that we don't want to cause the donkey pain. The ox is a מעלה גרה - he regurgitates his food, while a donkey does not. When the donkey hears that the ox is eating a second breakfast and he is not, he will feel pained. In order to prevent this the Torah forbade us from plowing with the two animals together.
To whom are we showing sensitivity? A DONKEY! The lowest of animals. When you want to insult someone in Modern Hebrew, the custom in these parts is to call him [affectionately] a חמור! Oyyyyy sweet friends, if we have to be careful about insulting a donkey - how much more so must we be careful not to insult or offend a person.
[The gemara in Bava Metzia 85a, relates that Rebbe Yehuda Hanasi accepted upon himself 13 years of suffering because he once insulted a calf. The calf was running away from the shochet and hid under Rebbe's kapote. Rebbe said "זיל לכך נוצרת" - Go, that is why you were created. For those words spoken to a calf [which were actually true] he suffered for 13 years. נורא נוראות].
Many years ago, Hagaon Rav Avraham Genechovski Ztz"l used to give a weekly shiur in Yeshivas Chebin. One week, the shiur was on the sugya of הנותן גט מתוך קטטה - One who gives a get to his wife as a result of a quarrel. The Rav arrives and out of the blue and to everyones surprise, he said, "Since Chanuka is coming up, I will give a shiur on inyanei Chanuka". He did but nobody could understand why he changed the topic of the shiur. After the shiur, the present Tolna Rebbe Shlita [who was a talmid at the time] was asked by HaRav Yehuda Rabinowitz ztz"l a maggid shiur in the yeshiva, what the shiur was about. He told him "Chanukah". Rav Rabinowitz said humorously "Maybe next week he will give a shiur on Pesach?!" The next week the Rav continued talking about Chanukah and the next week after as well, to everyone's surprise.
The Rebbe Shlita's chavrausa had a theory. There was a boy whose parents were going through an acrimonious divorce and Rav Genechovski didn't want to talk about the topic, even in the context of learning, in order not to cause the boy more pain than he was already experiencing. Some time later, the Rebbe Shlita asked Rav Genechovski if this was the reason and he confirmed that it was.
[Based on the words of the Rebbe Shlita, Motzaei Shabbos Parshas Ki Teitzi תשע"ג]
לרפואת ולזכות כ"ק אדמו"ר שליט"א