For those of us with a poor grasp of time, who can still recall when a night at the pub could be sharply revisited by a Proustian wave of stale smoke arising from yesterday’s clothes, it can almost feel as if vaping crept up on us out of nowhere. One moment, it seemed, all the authorities had firmly agreed that Nick O’Teen was a creepy pusher hooking innocent kids on gaspers, and were pledging to legislate and tax cigarettes into oblivion; the next, great hordes of schoolchildren were apparently free to suck constantly on little vials of liquid nicotine with...