Most NYC subway riders are pretty blasé when panhandlers hit them up for cash between stations. When a panhandler announced he was collecting funds to build a time machine, riders chuckled at the odd request—until another man boarded the train and announced he was the inventor’s future self. He implored them not to give any money because time travel will ruin everything.
It sounds just like that X-Files episode (“Synchrony”) where a scientist travels from the future to stop his younger self from making the cryobiological compound that will one day enable time travel. But it’s actually an elaborate prank by Improv Everywhere.