...And in truth, the source of the phenomenon of lack of concern in the serious matter of causing our friends' anguish, is the effect of two causes:
1. We love to display our capacity to express our cleverness to such an extent that we become oblivious t any sensation of the pain that the expression can cause.
For there are sins from which a person derives bodily pleasure - such as in eating forbidden foods, when one does so with an appetite, or when one robs and steals on account of his lust for money. But there are sins that a person commits without deriving any material benefit, such as Sinas Chinam - the hatred of another person "for free" - when the other person did not do anything to provoke a desire in me to take revenge, yet I nevertheless bear a grudge of hatred towards him for no reason. Why does this happen?
In fact, chinam - חנם = does not refer only to something one acquires without payment. Rather, chinam is a derivative of the word chen - חן, grace [or, in this context, an intangible affitnity]. (The final mem in chinam is not part of the word's root, but is rather akin to the final mem in reikam ריקם - see Ibn Ezra Shemos 3.) In other words, I have an intangible affinity to this character trait without a reason and without a cause, its source being the yertzer ho'ra imbedeed within me that gives me an intangible affinity for certain sins. This is also the case in regards to lashon ho'ra and rechilus, in which one has no pleasure independent of the intangible affinity that he has with the sin...
A great man once witnessed two talmidim disputing an opinion of one of the Rishonim, each of them shouting at the other, taunting and mocking, that the other had no idea how to understand a Rishon, etc. Hee said to them: "You should know that by now you have completely forgotten the words of that Rishon, and your entire dispute is: 'Which one of you is the smarter one?' - that is the entire disagreement!'"
Sicha #7, זהירות בכבוד חברים
Sichos b'Avodas Hashem
R' Yaakov Y. A. Meisels