If you feel like an idiot in a dream, then such dream signifies the lack of self-trust. You do not feel confident in your own skin. The dream about someone being an idiot could symbolize the fact that you are very rude towards the others.
Dream dictionary: Idiot dream meanings
…Idiots in a dream, foretells disagreements and losses. Dreaming that you are an idiot, you will feel humiliated and downcast over the miscarriage of plans. To see idiotic children, denotes affliction and unhappy changes in life….
(See Tankard)
…To extract any definite information from an idiot as to his dreams is next to impossible, and after many and sundry vain efforts I have had to desist. From what I have been told, however, by one who had charge of an idiot, the latter used very often to dream he was being chased by something alarming, that he was in danger of being drowned, and that he had all his toys taken from him. The idiot was often ill after the drowning dream, and very fretful and bad-tempered after dreaming he had lost his toys. The grimaces and noises he made in his sleep were generally more shocking than those he made when awake often, indeed, most terrifying. Once, and that a day or two before he had an accident, he evidently dreamed he was flying, for he sat up in bed and flapped his arms up…
…(Dull-witted | Dummy | Idiot | Mug) In a dream, a tankard represents a housekeeper or a servant. A tankard or a mug in a dream represent the household servants who consent to sexual abuse or sexual relationship with their employer. Drinking from a tankard in a dream also means earning money through one’s servants or employees. A broken tankard in a dream signifies the death of one’s servant or employee. (Also see Mug)…