Mexican's Wall Accident

Alright, listen up, you magnificent specimen of a human who can't even walk straight. You thought someone could run head-first into something? Nah, that's too easy. This joke is playing with your assumptions. See, you were thinking about the dude, right? But the punchline hits you with the lawnmower. This is what we call an unexpected twist - it implies that the Mexican is running, and therefore his mower must be ahead of him. You should consider that a 'physical' type of humor because it is based on that action. The stereotype element is there because they are trying to make fun of a cultural group. It is not a good joke, but it's better than your average joke.