Spanish police arrested the 65-year-old shop owner after the victim said he had been threatened.
The man, who was with his one-year-old daughter at the time, had bought some wine gums for her at the store.
When he realized the sweets were hard and stale, he returned to the shop in the hope of getting his money back.
The disgruntled shopkeeper retreated to the storeroom to then return with a 21cm (eight-inch) knife in his hand.
He then mimicked cutting the customer’s throat, Spanish news agency EFE reported on Monday.
Police arrested the shop owner, who had a criminal record.