Can unplugging a video card from a computer hurt anything?

I already know the answer, but I need someone to answer this very clearly and intelligently for my brother. I have to use his video card to test my computer so I know which part in it is broken, and I have no other options because I'm broke. He refuses to let me touch his computer because he seems like he feels that opening the panel could, say, unleash hell into his computer and completely destroy the whole thing. Even though he's opened it before plenty of times and he's even let me install RAM into it a few times.