Ernest Welde says he's been chased, swung at and even pushed by truck drivers, who disapprove of his side gig. From his phone, Welde records trucks that are parked for longer than three minutes with their engines still running, an offense in New York City.

"Every time I go out of my house, I am prepared for an assault," Welde, an environmental attorney by day, told CNBC. "You have to go out expecting there's going to be a confrontation."