I know which trick I'll play on my girlfriend on April Fool's Day. I will buy a wig and arrange it into a funny hairdo. I may make a lot of small plaits or I may lift the hair up and fix it with gel or wax. And I'll put a piece of paper with the words "Meet April Fool" written back to front and cover it with sweet cream in order it sticks to my girl's hair.

Then the night before April 1st I will put this funny wig on my girl's head when she is asleep. In order her sleep is strong I will stealthily give her some soporific. I even may put some funny colorful makeup on her face.

When she wakes up in the morning she likes to look in the mirror. This morning she'll wake up and when I turn to her to kiss her I will make a wild cry and jump out of the bed staring at her with fear.
Then she will quickly run up to the mirror and it will already be her turn to scream and shout :-) But as soon as she starts to pull her hair she'll pull off the wig and see that nothing bad has happened