I've had people very rudely try to take over my site and I've had people go to great lengths to try and stay on their own postage stamp sized site.
I got very tired of a fellow walking through my site and nearly under my awning. On a trip through I handed him my trash bag and said "If you plan on camping with us, you need to work for it". He laughed, took my trash and said "I guess I am really in your space". We had occasional pleasant conversation the rest of the weekend.
The opposite was a gentleman who was killing himself trying to keep his toad dolly off our site. The sites were very cramped and he would have no space with the dolly on his site and there was no place else to park it. I suggested that he run the tongue up under the back of our trailer to free up his site. If he did that under his MH it would block our table. It worked for both of us.
The key is courtesy. If someone respects my site and is in a bind, I'll do anything for them. If they are rude, I'll use a little passive aggressive humor and hope for the best. I'm not going to be confrontational, its just not worth it.