jackassume
Making a dumb guess that makes your brain look like a trash can. It’s like assuming without thinking, and then getting called out.
He jackassume’d that the pizza was free. It wasn’t. He got called out by the delivery guy.
She said the cat would nap all day. It ran around like a lunatic. She jackassume’d.
He thought the math problem was easy. It wasn’t. He jackassume’d and got it wrong.