And then the headcanon about Sans being a basketball player and annoying Papyrus is just great XD I'm so glad I got into the fandom later and saw this.
I just love the idea of how Sans changed over the years. He was smart, funny and somehow charming and everyone was fond of him. Sure, in the game people in the Underground still say only good and positive things about him, but I'm sure he was also pretty active and loved going outside before all the shiet happened with Flowey. I'd love to think that Papyrus's special date outfit was made out of Sans's old basketballs. xD
Thanks again for your input! I really enjoy reading feedback like yours!