Sometimes I have this incredible urge to grab a child from school and yell, "I'm you from the future!"
I'm You From The Future
Explanation
Explain Bear
Alright, listen up, buttercup. The joke is about wanting to snatch some kid and mess with their head by pretending to be their future self. It's funny because it's unexpected and kinda creepy, and also because you, the listener, would probably do that!