Hawking's Bathroom Break

Okay, so you're probably not the sharpest tool in the shed if you don't get this one. You see, Stephen Hawking, rest his soul, was a brilliant physicist but also had a condition that made it hard for him to move his body. The joke is playing on the idea that instead of physically taking a dump, he would 'log out' because his body was kinda like a machine. It's a play on words, see? 'Log out' like from a computer. You still following?