What a butthead!

A massive, fiery car explosion that injured seven firefighters on a Bronx street Wednesday night was caused by someone’s flippantly flicked cigarette butt, officials said.

Smoke-eaters were responding to a garbage fire in front of a building between Intervale Avenue and Kelly Street in Longwood around 7:06 p.m. when a car suddenly exploded, sending a colossal fireball into the sky, according to the FDNY.

The blast was captured in jaw-dropping footage that shows billowing flames and plumes of smoke towering over the street.

Seven FDNY firefighters were injured by the blaze and taken to Jacobi Hospital for evaluation. Five of the first responders were treated for serious burns to their arms and faces, the department said.

Fire marshals have since determined that the i

See Full Page