The best April fools jokes that i've done are:
Snack Switcheroo- You get a packet of chips (i would recommend cheese puffs), and then open the packet and replace it with carrot sticks. Seal the packet with double sided tape or glue. Just wait till your victim opens the packet and finds those carrot sticks instead of cheese puffs.
"Sponge" Cake- Get 5 rectangular kitchen sponges and stack them. Frost the sponge stack like you would do with a cake, Around the edges, put sprinkles to hide a bit of the color. Then serve the cake, let your victim cut the cake and get a nasty surprise.
I hope you like those ideas, WADDLE ON CP!!!