Below is a list of my favorites! Please comment to share any I have missed.
It is illegal to die in the Houses of Parliament
It is an act of treason to place a postage stamp bearing the British monarch upside-down
In Liverpool, it is illegal for a woman to be topless except as a clerk in a tropical fish store
Mince pies cannot be eaten on Christmas Day
In Scotland, if someone knocks on your door and requires the use of your toilet, you must let them enter
In the UK a pregnant woman can legally relieve herself anywhere she wants, including in a policeman's helmet
The head of any dead whale found on the British coast automatically becomes the property of the King, and the tail of the Queen
It is illegal not to tell the tax man anything you do not want him to know, but legal not to tell him information you do not mind him knowing
It is illegal to enter the Houses of Parliament in a suit of armour
In the city of York it is legal to murder a Scotsman within the ancient city walls, but only if he is carrying a bow and arrow
Most ridiculous foreign laws:
In Ohio, it is illegal to get a fish drunk
In Indonesia, the penalty for masturbation is decapitation
In Bahrain, a male doctor can only examine the genitals of a woman in the reflection of a mirror
In Switzerland, a man may not relieve himself standing up after 10pm
In Alabama, it is illegal to be blindfolded while driving a vehicle
In Florida, unmarried women who parachute on a Sunday could be jailed
In Vermont, women must obtain written permission from their husbands to wear false teeth
In Milan, it is a legal requirement to smile at all times, except funerals or hospital visits
In Japan, there is no age of consent
In France, it is illegal to name a pig Napoleon