Yes it is HARAM because of the origins of April Fool's Day.
It was around a thousand years ago that Spain was ruled by Muslims. And the Muslim power in Spain was so strong that it couldn't be destroyed. The Christians of the west wished to wipe out Islam from all parts of the world and they did succeed to quite an extent. But when they tried to eliminate Islam in Spain and conquer it, they failed. They tried several times but never succeeded.
The unbelievers then sent their spies in Spain to study the Muslims there and find out what was the power they possessed and they found that their power was TAQWA. The Muslims of Spain were not just Muslims but they were practicing Muslims. They not only read the Quran but also acted upon it.
When the Christians found the power of the Muslims they started thinking of strategies to break this power. So they started sending alcohol and cigarettes to Spain free of cost. This technique of the west worked out and it started weakening the faith of the Muslims in particular the young generation of Spain. The result was that the Catholics of the west wiped out Islam and conquered the entire Spain bringing an end to the EIGHT HUNDRED LONG YEARS' RULE OF THE MUSLIMS in Spain. The last fort of the Muslims to fall, was Grenada (Gharnatah), which was on the 1st of April.
From that year onwards, every year they celebrate April fools day on the 1st of April, celebrating the day, they made a fool of the Muslims. They did not make a fool of the Muslim army at Gharnatah only, but of the whole Muslim Ummah. We, the Muslims, were fooled by the unbelievers. They have a reason to celebrate April fool day, to keep up the spirit.
Dear brothers and sisters, when we join in this celebration, we do so out of ignorance. If we had known about it, we would never have celebrated our own downfall.
So now, that we are aware of it, and now let us promise that we shall never celebrate this day. We should learn our lesson from the people of Spain, and shall try to become practicing Muslims, never to let anybody weaken our faith NOR FOOL ( OR MAKE A FOOL OF ) US ANY MORE.
And even if not because of it's history, lying is Haram. Joking is considered lying also if it isn't true (unfortunately probably all of us still do this). Even if you were to feel content with just "joking", it is a Kafir "celebration", so by celelbrating it, we are imitating the Kuffar. We are supposed to separate ourselves and set examples with our actions, not drop ourselves to the level of the Kuffar. Our objective is to do Dawah by our actions, and this can't be done if we are blending in and adjusting our lifestyles with the Kuffar.
