Tin Foil Hat, also tinfoil hat, or tfh
, a general term for a piece of headgear made from one or more sheets of tin foil, aluminium foil, or other similar material. Some people wear the hats in the belief that they act to shield the brain from such influences as electromagnetic fields, or against mind control and/or mind reading. The concept has become a popular stereotype and term of derision; in Internet culture, the phrase serves as a byword for paranoia.
that guy is so paraniod he needs a tin foil hat.