Sri Caitanya Mahaprabhu warned His devotees not to commit Vaishnava-aparadha, an offence at the feet of a Vaishnava, which He described as the mad elephant offence. When a mad elephant enters a beautiful garden, it destroys everything, leaving a barren field. Similarly, the power of Vaishnava-aparadha is so great that even an advanced devotee becomes almost devoid of his spiritual assets if he commits it. Since Krishna consciousness is eternal, it cannot be destroyed altogether, but advancement may be checked for the time being. Thus Vaishnava-aparadha is one kind of impediment to devotional service. When one commits an offence at the feet of a Vaishnava, one must immediately apologize to such a personality so that his spiritual advancement may not be hampered.
Source: A.C. Bhaktivedanta Swami Prabhupada (2014 edition), “Srimad Bhagavatam”, Fifth Canto, Chapter 01 – Text 05