Chris Brown -- My Muscle Car's Got NO Muscle

Chris Brown suffered the ultimate vehicular humiliation Thursday ... as he tried to act super-cool in a classic whip that couldn't get off the dime.

A full crew and huge crowd gathered as Brown prepared to shoot his music video ... the singer cruising down Figueroa in L.A. in a super-sweet '60 Chevy Impala.

The engine repeatedly turned over but there was no ignition, as a clearly embarrassed Brown stoically turned the key ... with rapper Compton Menace riding shotgun.

Eventually ... the whip moved ... but oh so slowly.