Kathryn Dowse, 21, insisted that trainee Andrew Gilbert should mop the floor at the branch in a supermarket in Heywood, Greater Manchester, the tribunal had heard.
Mr Gilbert, 24, also said that Ms Dowse was "rude and patronising" towards him.
The tribunal in Manchester ruled that Mr Gilbert was the victim of sex discrimination by the Midland Bank, who sacked him after complaints by Ms Dowse before he had completed his probationary period.
The tribunal chairman, John Goodman, said: "The inference we draw on the evidence is that Kathryn Dowse perceived Mr Gilbert as a young, assertive man who posed some sort of threat to her authority as a relatively inexperienced, young, female manager. One illustration we find illuminating is her insistence on him participating in the mopping of the floor."
The tribunal ruled the bank had been "unreasonable and unfair" in the treatment of Mr Gilbert, of Handforth, Manchester, who now works as a theatre box office manager in Crewe, Cheshire.
They said he had been treated less favourably than the three other female employees at the branch, and the senior manager said to have authorised his dismissal had acted solely on information from Ms Dowse and made no attempt to speak to Mr Gilbert.
Mr Goodman said in his ruling that the Midland Bank spoke in its literature of steps it took to prevent discrimination. But he said: "No matter how pious and well intended those sentiments are, the employer must also take practical and active steps to ensure they are implemented. I can say quite emphatically we do not regard the conduct of the bank as indicative of taking such steps as were reasonably practical to avoid discrimination."