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1.
A person who continuously changes the speed at which they drive regardless of the speed limit.

An example of a speed fluctuator would be someone driving on a 55 mph highway fluctuating their speed between 50 and 60 mph. This very annoying behavior makes it impossible for the poor person stuck behind them to use their cruise control.
by Daren Hathaway January 03, 2008
 
2.
A person who continuously changes the speed at which they drive regardless of the speed limit.
An example of a speed fluctuator would be someone driving on a 55 mph highway fluctuating their speed between 50 and 60 mph. This very annoying behavior makes it impossible for the poor person stuck behind them to use their cruise control.
by Daren Hathaway December 05, 2007