Forbidding Airlines from Imposing Ridiculous Fees Act of 2021 or the FAIR Fees Act of 2021 This bill directs the Department of Transportation to prescribe regulations (1) prohibiting an air carrier from imposing specified fees relating to a flight in passenger air transportation that are unreasonable or disproportional to the costs it incurs, and (2) establishing standards for assessing whether such fees are reasonable and proportional to those costs.