Family differences can be hilariously funny.
Growing up, in my family, when you sat somewhere, you stayed there.
If you got up, you came back to the exact same spot.
If someone offered you their spot, they were being polite. You would reciprocate by graciously turning them down.
You would say "Thank you, that's very nice of you, but that's okay, I'll just grab a chair.". 
That was our system of manners and respect. You didn't take advantage of someone elses generousity.

Spots were a big thing in our family.
For years, all of us had a spot on the couch (it was an 8' wide, homemade couch).
- Mom had her spot on the couch on the end
- I had mine near Mom
- Sonny and Dad sat further away at the dining room table. If they sat at the couch, they had an issue to resolve.
- Linda, Grandfather, Grandmother, and various guests had their spots at the end.
- Kelly was a spot stealer, she never chose a spot. She would either stand in front of us, or sit in the middle of the cushons, to take up two spots.
You wouldn't believe how many arguments having a spot picked out, resolved with a family of six living in a very small house.
But all families are not created equal.
I noticed at a BBQ yesterday, that everyone who left the living room came back to sit in a different spot.
There was an easy chair in the living room, and almost everyone sat in it.
One person left their spot in the easy chair to get some pie.
He had to sit on the floor, because in the minute he was gone, someone had taken the easy chair.
In our family, that would have meant WAR !
At the BBQ I had my spot on the couch in the living room.
It was marked by my camera, and my sunglasses, and by golly, if someone took it, that would have met the wrath of Jim.
"HEY, GET OUT OF MY SPOT !".
Someone offered me her spot at the table
I wouldn't take it. Neither Sonny or I will do that. We pick our spots. That's was just our family's way.
No, I didn't slide over because Dustin and Becky got up.
No, I didn't take the easy chair when Gma, Paul, and Emily got up. Robert may have sat there too. lol.
And most of all, NO, It didn't mean I'm a pervert who wanted to cuddle up to the 13 year old, budding, Jennifer.
HAHAHAHAHA!!!!
It simply meant, I was not taking some else's spot.
And by the way, thank you all very much for reading this. You have been very kind.
LOL.