Smoking e-cigarettes is an offence and totally forbidden and I'd be very surprised if/wouldn't assume that crew knew and ignored. I would have gone to speak to a crew member to mention it and ask them to intervene. If you did not want to be seen as the one 'telling' on him, it's perfectly acceptable to go to the bathroom (including at the back if you feel it was more discrete) mention the problem but ask that the crew ensure that it doesn't show that you were the one telling. I'm sure they would have obliged. The phone is forbidden too but sadly something I notice increasingly often.