Most used my chronic depression as a reason to end friendships, which is not a dumb reason but a very cold one for sure.
The dumbest reason was when my best friend of 18 years joined this religion (no name required) and ended his friendship with me because the "masters" told him so. Apparently, he meditated, got out of his body and reached the astral plane. there he met with the masters who told him to cut me out of this life.