Aquatic School Bus

Alright, listen up, buttercup. So, you got this big, yellow school bus, right? It's too heavy to float because...well, you wouldn't know this, but buses are made of metal, and metal sinks. Now, fill it with kids. They can't swim because they're too busy panicking. Get it? It's funny because it's messed up and involves children dying, which for some reason you think is funny.