I am surprised, fun can be fun - when it is planned... Having loose objects endangers everyone in the aircraft. The only fun in this case was someone being an idiot and placing thier friends at risk - WHY. Was it just to feed an ego?
If it had been a boy racer rather than a pilot would the attitude be the same? Would it still be classed as "fun"?
To me its the same as someone driving a car to the limits, its a risk which can be avoided.
Aero's are great fun and I agree about the comments about zero g loading. However aero's should be planned. Part of that planning should include making sure there are no loose objects, especially a can of coke in your mates hand.
And before someone asks, I have flown a lot of hours for fun doing aerobatics.... It was always planned and prepared for.