frolic and detour

Definition from Nolo’s Plain-English Law Dictionary

Employee conduct that is outside the scope of employment and is undertaken purely for the employee's own benefit. Although an employer is generally liable for the acts of its employees, an employer is not liable for damages employees cause while on a frolic and detour. For example, a delivery company could be liable for injuries one of its drivers causes while racing to make a delivery; it probably would not be liable if the same driver shot a guard while robbing a bank on his lunch hour.

Definition provided by Nolo’s Plain-English Law Dictionary.