He used his chrome horn to tell the slow car to move.
chrome horn
idiomThe front bumper of a car when used to bump another vehicle, usually to inform the driver of the other vehicle that the first car would like to pass.
Origin
disputed originThe phrase most likely originated during NASCAR broadcasts in the 1970s, when stock cars still had chrome bumpers.
The driver in front refused to speed up, so she gave him a quick nudge with her chrome horn.
Frustrated by the sluggish pace of the traffic, the impatient motorist deployed his chrome horn to signal his intent to overtake the dawdling vehicle ahead.