The origins of April Fools day appear to be lost in the mists of time although suggested pre-cursors to this strange custom have similarities in the Roman festival of Hilaria where jokes and laughter seemed to be the order of the day.
In the UK, the first recorded mention of such a day appears during the 14 century in Chaucer's Canterbury Tales.
In the UK & many other European countries jokes should only be played up to 12 noon, afterwards the joke is on the person who instigates it, whilst in other countries jokes can be played all day.
In my youth I remember the day being divided into strict segments: Jokes up to 12 noon, tripping over up to 4pm after which you could kiss the person of your choice for the remainder of the day!
Have a jovial April Fools!