A glass of water at a restaurant is usually free, but one generous diner decided that two glasses of water called for a generous tip.
A mysterious patron later identified as a popular YouTube vlogger left a $US10,000 ($NZ15,260) gratuity at Sup Dogs in Greenville, North Carolina on Saturday.
The customer walked in, ordered two glasses of water, and then abruptly left.
The waitress, Alaina Custer, was shocked to return to the table and find $10,000 in cash, the MailOnline reported.
Custer kept most of the cash while the rest was split up among the other waitresses at the restaurant.
"Good people are still doing good things these days so I thought it was pretty cool." said owner Bret Oliverio.
"I've seen some really big tips but not $10,000 this was out of the blue, once in a lifetime, it'll never happen again in my lifetime."
Locals later determined the identity of the mystery diner - Jimmy Donaldson, who is also known by his online persona, MrBeast.
MrBeast is a YouTube personality who has nearly 9 million subscribers.
His YouTube videos - usually zany stunts designed to get a reaction - routinely generate tens of millions of views, according to Business North Carolina.
Last December, MrBeast posted a video in which he is shown handing his mother $100,000.
The video generated more than 5 million hits.
Another popular video showed MrBeast tip a pizza deliveryman $10,000 - just as he did the waitress at Sup Dogs.
Last May, he reached a milestone - 500 million total views of his videos.
YouTube personalities with millions of subscribers earn millions of dollars a year thanks to their large following and the desire of advertisers to broaden their audience.
Experts caution against overuse and social media diagnosis.