Laurence Vonderdell, 50, entered the Bournemouth town centre branch of Barclays and approached one of the tills holding the banana covered with an orange plastic bag.
He then pointed it at the cashier, telling her: “This is a stick up, give me the cash.”
The cashier handed over £1,100 in £20 notes, which Vonderdell took before walking out of the store.
But shortly afterwards, he handed himself in at Bournemouth police station.
Mr Vonderdell was sentenced at Bournemouth Crown Court on Monday after admitting robbery and possessing an imitation firearm.
He was sentenced to 14 months in prison.
Det Cons Andy Hale, of Bournemouth CID, said of the robbery, which happened on March 25: “Even though the defendant handed himself in shortly after this incident and the cash was recovered, this must still have been a very distressing incident for the cashier involved.”
