There is a good answer at the Skeptics StackExchange here. Its three most relevant references are:
Wilson v Southwest held that being attractive and female is not a BFOQ for being a flight attendant, even when the company marketed themselves using female sexuality:
sex does not become a BFOQ merely because an employer chooses to exploit female sexuality as a marketing tool or to better ensure profitability
Most scholars believe that the BFOQ exception would not apply to Hooters servers for the same reason. The job is serving food, and the sexualized nature of the service is just the manner in which they do the job, not a requirement of the primary job itself.
Hooters has never had a discrimination suit go to trial, however has been sued and settled out of court multiple times.
Employment discrimination based on gender has been allowed only in cases where the primary product being sold (not merely the manner of delivery of the primary product) requires a particular gender. One example would be sexual entertainment. This would include strip clubs, modelling agencies, Nevada brothels, etc.
I'll say it one other way.
Simply offering attractive female service as part of a business strategy is not enough to trigger a BFOQ exception.
To allow a BFOQ defence based on an employer's desired manner or means of achieving its primary business purpose would render the statute inoperative, and the BFOQ exception would "swallow the rule" Phillips v. Martin Marietta 400 U.S. 542 (1971).
(This paragraph taken from here.)