You Chose Poorly
Introducing a new cat to your home can be daunting to both the new owner and the new pet. The OP’s friend was a tad bit nervous about adopting a cat from the shelter, and it turned out that they had very good reason to be. The first thing the cat did wasn’t find a place in the corner to hide.
Instead, it woke up that morning with nothing but violence on its mind. Look, you crazed furball, your owner rescued you from the shelter. The least you could do is show some appreciation and now try to stab your owner the second you arrive.