“Tin foil hat” has become a stereotype for a conspiracy theorist. A joke was posted on Reddit—Shower Thoughts on January 4, 2018:
 
“What if tinfoil producers create conspiracies so people buy their tinfoil?”
   
     
Wikipedia: Tin foil hat
A tin foil hat is a hat made from one or more sheets of aluminium foil, or a piece of conventional headgear lined with foil, worn in the belief or hope that it shields the brain from threats such as electromagnetic fields, mind control, and mind reading. The notion of wearing homemade headgear for such protection has become a popular stereotype and byword for paranoia, persecutory delusions, and belief in pseudoscience and conspiracy theories.
 
Note that “tin foil” is a common misnomer for aluminium foil; packaging metal foil was formerly made out of tin before it was replaced with aluminium.
   
Reddit—Shower Thoughts
What if tinfoil producers create conspiracies so people buy their tinfoil?
submitted January 4, 2018 by paulusmagintie
 
Twitter
Shower Thoughts‏
@Thoughts4Shower
What if tinfoil producers create conspiracies so people buy their tinfoil?
#showerthoughts
3:23 PM - 4 Jan 2018
 
Twitter
RandomFun!‏
@RandomFun_
What if tinfoil producers create conspiracies so people buy their tinfoil?
3:26 PM - 4 Jan 2018
 
Twitter
Joseph Maloney‏
@Brosef_Joseph
What if tinfoil producers create conspiracies so people buy their tinfoil?
3:41 PM - 4 Jan 2018