There are six categories of offenses committed against a devotee: to physically offend, to criticize, to envy, to disrespect, and to become angry with him or to make him angry. These offenses implicate a person with unatoneable sin. Such offenders are condemned to take birth as pigs in their next life, even though they may chant the holy names of the Lord.
As it is stated in the Skanda Purana:
nindakah sukaras caiva
saphalam nirmitam hareh
sudhyanti sukara gramam
sadhun sudhyanti nindakah
“Lord Krsna has rightly decided to turn criticizers of His devotees into stool-eating pigs in their next life, because pigs clan villages by eating stool and rejected garbage. Similarly by criticizing His devotee, they purify the offended devotee by taking his remaining sins.”
[Sri Krsna Balaram Swamiji, My Mission, KBS0038]