energiser
For flybys, there is usually no doubt who the perpetrator was- of course DFDR info has been used as evidence in any case. For Cabin Crew flying, the only way you could prove anything is either to get somebody to admit it (highly unlikely as it would almost certainly be an instant P45 for all involved), or for someone to say something silly over the radio. Any CVR info will be long-gone by the time the aircraft lands.
For DFDR data to be any use, you would have to prove who was manipulating the controls- virtually impossible.
There have been plenty of recent examples of flybys/buzzing houses etc, so that obviously still happens. I happen to know that Cabin Crew flying the plane also happens, but is kept much quieter than in times past- other than that, I agree with MOR/Hew Jampton.