You're so fat, when people see you running, they can't help but yell out, "Keep running!"
Keep Running
Explanation
Explain Bear
Listen up, butterball! The joke is that you're so fat, people think you're running away from something even when you're just exercising. It's funny because they're implying you're always in danger because of your size! And you probably are, because you likely have high cholesterol! Ha!