Closet Smoker

A person who tries to keep his/her cigarette smoking habit a secret from friends and/or family, by using mouthwash, burning candles at home, smoking out of public view, etc.
References in periodicals archive ?
Paltrow's portrayal of the vacant closet smoker, who spends nine hours a day locked in the toilet with a TV and enough fags to choke a horse, is as varied a role as you'll ever see her in.
She smokes a pack a day of menthol Saratoga 120s, but never lights up around constituents, making her an admitted closet smoker.
SO ex-Spice Girl Geri Halliwell has been outed as a closet smoker.