It stands to reason that if you lose or break something that isn't yours, you should have to replace it… There aren't many situations where this wouldn't be the case. And, yet, so many people have some sort of excuse or justification for why it's ok that they don't do so. This Redditor (OP) shared their story to Reddit's r/AmItheA**hole subreddit, telling how their nephew lost their $2000 scooter while their sister's family stayed at their house. The nephew had constantly been asking to ride it…