A single word for a signalling method?

Question:
A vehicle following another signals or forces it to immediately pullover to a side by hitting it lightly from behind. This may be done because the driver in front disobeys all other forms of signals and continues to drive speedily without pulling over. Is there a single word / phrase that can be used to describe this situation where one driver signals another to stop the vehicle immediately by bumping lightly from the rear?

Answers:

When a cop stops for speeding,what is the best answer so he might not issue summon?

ILLEGAL!

HID headlights for my Big rig??

also dangerous to you health. Do it to ME and you will be punished severly!

Parallel parking help!?

Road Rage, eh ?

do you hover over a toilet seat in a motorway service station or put paper down?

Wrong is the best single word to describe the action taken.
Best phrase: Road rage from a confused self imposed cop.

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homocidal

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