Grim Adventures Of Billy And Mandy (the) Easter Egg - Irwins House

In the episode where Irwin goes to the museum and is visited by his mummy grandpa, while he is going to his house, look at Irwin's house at the front, it looks like Dexter's house from "Dexter's Laboratory." That means the creator of Dexter's Laboratory, who made Foster's Home for Imaginary Friends, are somehow friends.