A brazen thief carjacked a yellow cabbie at knifepoint outside a Chelsea hotel early Monday – before eagle-eyed cops spotted him uptown and eventually busted the joyriding bozo.
John Butler, 52, flashed a knife at the 55-year-old driver in front of the Courtyard by Marriott-Chelsea on West 30th Street near Seventh Avenue around 3:10 a.m., police said.
Butler, who is believed to be homeless, demanded the driver get out of the cab, according to police, which he did…