Coincidentally just seen this (hope link works - warning contains some fairly graphic photos)
https://www.facebook.com/andrew.hall.3910/posts/10100193309728068
There's a bloke a few rows in front of us who does it all the time. Never seen a steward anywhere near him.
It's a no from me. It can be as irritating as cigarette smoke, even if it isn't damaging. Bloody great clouds of sickly strawberry flavoured fog.