Give it another decade and what he has implied you were doing likely will not even be illicit any longer. In the short term, especially if you are quitting analogs, vape publicly and if people are curious, share with them how vaping has helped you quit. As others have mentioned, that typically garners lots of support and enthusiasm from people.
Bigger picture, try not to let people get to you like that. Easier said than done I know but you know where you stand. This should blow over (no pun intended) quickly enough. If this could affect your reputation and professional prospects at school, then that would warrant a serious conversation with him. If he is a decent human being, he will respect your wishes.