It wasn't like he wasn't liked in the mansion.
The other Smashers just had a hard time relating to him.
With the happy-go-lucky heroes and the downright evil villains, he had a hard time fitting in. He was neither, someone who kept a completely neutral stance of everything and preferred to make his own opinions than blindly follow the herd of "he's evil because he kidnaps the princess!" or "he saved her from the evil monster so he's a hero!"
He personally saw both points of view. Yes, it was a good thing that Mario saved Peach since the Kingdom was screwed without her, but Bowser was just looking for a mother for his children. Did he think Bowser was an idiot for his methods? Yes, but Mario could be an idiot too for putting his life in constant danger.
This made him simultaneously the hardest and easiest person to get along with thanks to his beliefs. He wasn't sarcastic because he disliked anyone - it was just his personality. The flawed, warped personality of his "twin".
Sometimes he wondered what would have happened if Pit hadn't shattered the mirror. If he truly would have been an evil clone of him. It was an interesting thought, but he never entertained it longer than a few minutes. That would have meant his freedom would have been stripped away - permanently aligned with one side. He personally liked being unaligned. He sided with whoever's interests lined up with his, the rest of the world be damned.
"I can't believe you're hanging out with Wolf, Pitto! He's the bad guy!"
"Why would you bother talking to that annoying hedgehog? Goody two-shoes doesn't know when to keep his mouth shut."
Dark Pit could only shrug. "Unlike you I see other points of view."
AN: No idea where this came from.
At least I'm writing though.