Still with all of that it was kind of a throw away line..
You'll kill everyone!
But Ice Cream Cake!

Doc was witnessing somebody stood on his own grave, it freaked him out.

Would it blow your mind to dig yourself up?
I'm.I'mdoing something in here.

I think the ground re-solidifies after a couple weeks, especially if rains.
When we're thinking about our own brain, would that be a mental paradox??

You don't think it's disrespectful to walk on a grave?
We have to show the world that not all of us are like him: Henning von Tresckow
.

i thought Doc was just trying to read the grave. Although it would be kind of funny if Marty standing on docs grave somehow upset the 70 year old spirit of Emmett Brown lol.

I've always wondered why that.
I just thought it was bad luck or the ground was soft there and it would cave in or damage the coffin somehow.

Because it's considered disrespectful to the deceased and improper etiquette to stand on top of a grave.