Electronic cigarette smokers sometimes explode, too.

Earlier this week, 23-year-old Krystal Feldsherov assaulted a woman who'd asked her to stop vaping on the C train, according to police. The grievance sparked a verbal dispute between the two riders, leading Feldsherov to allegedly punch the complainer in the face near the High Street stop in Brooklyn.

The victim suffered swelling and bleeding to her upper lip, and was transported to NYU Langone in stable condition, police said. Feldsherov was arrested and charged with assault.

Earlier this year, the city upheld its ban on vaping anywhere that cigarettes are banned—which includes subways.

For more on the potential perils of e-cigs, here's our feature from 2013 on the still-emerging industry, and here's our advice for dealing with occasionally violent e-cig scofflaws.

