Is it normal to get angry when someone borrows your pen but doesn't give it back?
It's not that I particularly care about that pen so much, if they'd have asked if they could keep the pen I'd have given it to them without a second thought. It's just the principle. I showed them the (admittedly small) courtesy of lending them a pen, but then they don't bother to show the (equally small) courtesy of giving it back. I just feel it's disrespectful not even to show that small bit of thought and consideration in giving me back things I lend to them.