Block door with a see through plastic wrap. Then wait and watch who gets bounced back on opening the door.
Attach a rope to the back bumper of target's car and tie a collar in such a manner so that it drags on the ground. For more fun can try putting that collar around a stuffed animal. For a good dose of fun ride along and watch the funny reaction of other drivers on the road!
Record the morning news telecast of the rainy day when schools were closed due to heavy down pore. Then play it back on April 1st in the morning while the kids are getting ready for school.
Draw moustaches on the face of the person whom you know is a sound-sleeper. Use an eyebrow pencil or other make-up. No markers please, they're too hard to remove!!
Place small water balloons in the toe your victims' shoes in such a manner so that it's not visible in the first glance. They'll get a chilling surprise! (More expensive the shoe, the more will be the fun but it should be avoided to prevent a ruckus)
Put some bubble wrap in front of or behind the tyres of the victim's car. When they back out of their parking space, a large pop will be heard, and then he/she will wonder what they hit.
Tie one end of a spool of ribbon to your victims doorknob with a note stating, "Follow the Ribbon." Then wind the ribbon all around their room, bed, desk, even all over the house. At the ending point of , attach a note "So finally you joined the fools league!"