It seems like the original post and half the responses here are yet another reason why pool players are viewed in such negative light, which helps diminish the sport.
Who wants to go play in a pool room where some guy is going to out of nowhere freak out on you, legit or not, rather than talk to you like a human being... Or where some business customer takes it upon himself to fling pool balls at you because they feel some sense of entitlement that really only the owner and employees should have.
1) People will do stupid things, players do it, bangers do it, and it happens in and out of the pool room... If you can't accept this, life is going to be long and miserable.
Yes it's rude to stand in a spot that others need to occupy, but it's also rude and a bit nuts to just yell at them without so much as trying an "excuse me" or two. Something more effective might be actually explaining etiquette to the offender because it's likely they are not aware of their behavior (as was pointed out)... And if they fail at that point, then get the room manager.
It's not your room, you rented the table, not the entire room, and not the right to try to scare customers off.
2) A couple of people promoted the idea of jumping a ball at the offender. If I was the owner and caught that happening, I'd be glad to help the police have battery charges pressed against the offender. This behavior is actually psychopathic.
3) It's easy to blame league players for bad behavior, but it's not just league players who cause issues, any unknowing person can, any moron can. It's often that I see the best players in the room blocking their neighbors from stepping in to shoot, rushing ahead of their neighbor to shoot when it's obvious the other guy was already getting down for their shot, sticking their backsides in a the next-door shooters face because they don't want to wait 5 seconds for the guy to finish his shot, and throwing tantrums after missing a shot while other players trying to shoot, and so-on... It's as common as air.
Normally I wouldn't bother posting in a thread like this, people are allowed to vent over whatever, but as someone who wants pool to be taken seriously I felt it was worthwhile to point out what a detriment this behavior is.