Movie Graves vs. Real Graves

Alright, you smooth-brain, listen up. You're clearly not a gravedigger, but you've watched enough horror movies to think it's an easy job. Well, guess what? It ain't! This person in the joke is talking about how digging a grave is hard work, unlike in those unrealistic movies. It's a morbid self-deprecating observation about the discrepancy between fiction and reality.