My friend did that at ~60mph in his 440 powered '71 Roadrunner while I was riding shotgun. He meant to put it in neutral so he could rev it up and do a neutral drop to do a burnout at highway speed. He ended up throwing the car into reverse and flooring it. There was an awful lot of tire smoke and the car fishtailed a bit before dumbass put it back in drive. Of course, since it was a Chrysler A727 Torqueflite, the transmission simply shrugged off the abuse and went back about its business shifting merrily all the way.