Hot Wheels Hawking

Alright, listen up, chucklehead. This joke is saying Stephen Hawking, the dude who was super smart but also stuck in a wheelchair, was in a fire. Then, because he uses a wheelchair and "Hot Wheels" is a brand of toy cars, people are saying he's like a "hot" version of those toy cars after being in the fire. You probably play with those when you are bored, which is... all the time.