Lack of Training
Hired him and have him a chance to work in IT field and learn and grow. Time goes on and positions change, he no longer reported to me, and to cover his own ass with his new boss he told him and his boss (my boss) that I never trained him. Ever.
He worked with me for two years prior to this incident and every time I do training I have it in email and they have a formstack to fill out acknowledging the training etc etc. anyway they flat out told them that to my face.
Never again. Story credit: Reddit / captthulkman