He was crazy because of the speed he was travelling down a dual carriageway. If all the traffic in lane one is doing a steady 70mph and he goes bombing down lane two at 120 (minimum) the closing speed is so fast that if anyone in lane one moved out into lane two to perform an overtake he would be on top of them before either of them could do anything about it.
He was literally out of sight --> driving past us --> out of sight.
Just because it's legal doesn't mean it's safe or sane.
If you want to go that fast do it on a track or a runway where you're not going to endanger anyone else's life.