*Note that some of these examples exclude certain states.
Although frowned upon, cannibalism is not actually illegal. The part that is illegal is if the body part that is eaten was stolen. As in the victim was murdered or the body part was removed without warrant.
Your parents probably told you when you learned to drive that it is illegal to drive barefoot. This isn't the case. It is a good idea to wear shoes though in case of an accident or emergency that you would be more protected when wearing shoes.
Note that you can receive a ticket if your lack of or choice of shoes is what caused an accident.
Owning a Flamethrower
Private ownership of a flamethrower is legal in every state in the United States other than California. Surprising, considering flamethrowers shoot hot flames as far as 25 feet.
Counting cards is not illegal. Although, casinos can deny service to anyone at any time. Therefore, they usually will deny players using this tactic to get an advantage over the house. In Atlantic City, however, they cannot ban players for counting cards.
Using a Radar Detector
In states other than Virginia or Washington DC, radar detectors are not illegal in standard vehicles. In commercial and military vehicles, however, they are illegal.
Note that radar detectors and radar jammers are different and radar jammers are illegal.
Owning a Machine Gun
Machine gun laws are very regulated but have never been illegal in the USA on a federal level.
Giving Your Children Alcohol
In 45 states in the United States, giving your children alcohol is legal in certain circumstances. In Minnesota, it is legal on private, non-alcohol selling premises with parental consent and when reporting medical need due to underage drinking for another minor.
For details on other states, check out this article.
As long as you are not selling them and are not prohibited from possessing a firearm, you can legally make your own. In addition, you do not need to undergo a background check or register the gun.
Corporal punishment is defined as physical punishment that is reasonable or not excessive and is technically legal at home in all 50 states. 19 states actually allow corporal punishment in the schools.
Owning a Tiger
Ever dreamed of owning a tiger? If you are in North Carolina, Alabama, Delaware, Nevada, Oklahoma, South Carolina, West Virginia, or Wisconsin, it is completely legal.
Warning Others of Police By Flashing Your Headlights
The federal judge ruled that flashing your headlights to warn drivers of speed traps is legal. They justified this decision by saying that it still serves the purpose of telling people to slow down and follow the law which is what speed traps are for in the first place.
As long as the numerical value and the money can be identified, it is fair game to draw on currency.
Removing The Tag From A Mattress
Although the tag might say it, it is actually not unlawful for you as the owner to remove the tag from your mattress. It is, however, illegal for salesmen or manufacturers to remove the tag. This is because in the “old days” they stuffed mattresses with unappealing materials and did not want consumers to know.
Riding in The Back Of a Pickup Truck
Although not recommended for safety reasons, in 20 states it is legal to ride in the back of a pickup truck. Other states have regulations and only a few restrict it completely.
Owning a Gun Silencer
Private citizens can legally purchase and possess silencers in 42 states but they are regulated. For more information on what states are legal, check out this article.
Marrying Your Cousin
In 11 states in the US, it is actually legal to marry your first cousin (being two people that share a grandparent).