It would take a VERY LONG TIME to actually hurt anything. THe redline on most engines are very consservative. More than anything, he'll reduce the spark plug life and on a hot day he could overheat the engine if he held it at 7000 while not moving for maybe 10 minutes. Iv'e seen a Toyota Camry engin with over 100,000 ,mlels on it run at redline wiht no coolant in it for almost 5 minutes before it seized up.

Most any sportbike motorcycle engine will last over 50,000 miles and bounce off 14,000 RPM limiters all the time. I've seen unmodified engines last over 20,000 miles when ONLY used at he racetrack.

But yes... it's VERY ANNOYING! and very childish unless you have a big V8, V10, V12 or something hgih performance worth listening to.