Tin foil hat
From Tardis Wiki, the free Doctor Who reference
Tin foil hats were a type of hat which, according to Lucie Miller, were "not a good sign at all". Tom Cardwell wore a tin foil hat. The Eighth Doctor naively supposed it might be the fashion at the time. (AUDIO: Blood of the Daleks)
Starkey, Alistair Gryffen and Jorjie Turner made use of tin foil hats to protect themselves from the Bodach's psychic energy. Darius Pike neglected to wear his, allowing the Bodach to send him to sleep and control him into giving up one of the Eyes of Oblivion. (TV: Dream-Eaters)
