Please accept my humble obeisance. All glories to Srila Prabhupada
In Srimad Bhagavatam verse 4.2.19 Maitreya Muni narrates to Vidura about how Daksha cursed Lord Shiva. He says
nishidhyamaanah sa sadasya mukhyair
daksho giritraaya visrjya shaapam
tasmaad vinshkramya vivrddha manyur
jagaama kauravya nijam niketanam
Maitreya continued: "My dear Vidura, in spite of the requests of all the members of the sacrificial assembly, Daksha, in great anger, cursed Lord Shiva and then left the assembly and went back to his home."
The word "vivrddha-manyuh" in the above verse means exceedingly angry. Anger is great danger and extremely detrimental to us in the path of progress. Anger makes us blind and deaf to suggestion and advice of even great souls. In the purport to above verse Srila Prabhupada very nicely explains why Daksha fell prey to anger. "Actually we can see that lust, anger and passion make a man crazy, even though he be as great as Daksha. The very name Daksha suggests that he was expert in all material activities, but still, because of his aversion towards such a saintly personality as Siva, he was attacked by these three enemies—anger, lust and passion."
Because of aversion to saintly person, he was attacked by anger and as a result he lost association of saintly people. So we should never offend others by our body, mind or words. His Divine Grace further mentions how Mahaprabhu compared offences towards Vaishnavas to a mad elephant. As a mad elephant can do anything horrible, so when a person offends a Vaishnava he can perform any abominable action. In the examples of Ashwattama and Karna also we find that both of them offended Pandavas who were dear devotees of Lord. So inspite of the fact that they were great experts in archery and possessed some good qualities, they ended up doing abominable actions. Ashwattama killed sleeping children of Draupadi, released Brahmastra to kill the child in the womb of Uttara. Karna spoke insulting words to Draupadi when she was dragged to Kaurava assembly after the Pandavas lost in the gambling. Though he was a great performer of charity, he was always envious of Arjuna.
So the point is service to Vaishnavas will bless us with ability to do great service to Lord and His devotees beyond our imagination and likewise offending the great souls will deprive us of whatever little good qualities that are present in us and make us do abominable actions. Therefore if we are not able to serve, we should atleast not offend or have aversion towards others.