Interestingly, most airlines' "contracts of carriage" allow them to refuse passage to people based on certain criteria.
For example, American Airlines clearly states in its contract of carriage that it can remove a passenger with an offensive odor not caused by a disability or illness; Delta Air Lines states that anyone who is barefoot, appears to be intoxicated or has a malodorous condition can be refused boarding.
If the problem persists even after you've spoken up, you can always report the situation to the airline after you land. Direct your complaint to your carrier's customer service department; you'll need the date of your trip and your flight number handy. Who knows? They might give you flight credits or bonus mileage points.
Travel guru Peter Greenberg is the travel editor of CBS News and publisher of PeterGreenberg.com.