Teenagers on mopeds that sit at the lights or at a junction constantly revving the engine... WHY??? Just let it tick over and then pull away when it's time to.
Boy racers in cars with loud exhausts that have to rev the engine right up as the pull slowly away.
Motorists that drive along a straight clear road with no turnings, no obstacles or other traffic ahead but constantly touch the brakes and drive at a hugely inconstant speed 20mph, 25mph, 15mph suddenly then back to 30 grrrrr
some 2 strokes require you to constantly rev them to keep them from stalling, not all though