My friend has been letting me park in the front of his house but yesterday a different friend's car was parked there. I'm pretty pissed right now.
Why are you pissed about something small like that?
He was nice enough to let me use the space but without any warning he's letting someone else park there now.
I can see why you're upset but that doesn't mean it's a good reason to be. You said it yourself, he was nice enough to let you park there and he didn't have to. You're pissed off about something that isn't even a real problem so try to just move on and talk to him about it if you need to.
It's not even that important. Just letting out some extra stress.
Well I'm glad you realize how small of a problem this is. You can talk to him and see if that car will be there for long if you want to though.