This is the question that was put to Tory leadership contenders David Davis and David Cameron during their debate on Woman's Hour on Wednesday. It's based on a largely American notion that your choice of pants says a lot about the sort of man you are, and in the early 90s it was routinely posed by magazine interviewers who had run out of things to ask. The question even has a political provenance: in 1992 a 17-year-old girl asked it of Bill Clinton during a live MTV programme. He said, "usually briefs", but it was the fact that the president had dignified such a query with a response - rather than his preference - that exercised his enemies.
When the two Davids were asked the question towards the end of the programme, neither appeared in the least ruffled. "Boxers," said Cameron immediately. Davis, presumably because he felt the need to take an opposing position, thought for a moment and said, "Briefs." Perhaps he just paused to check.
So who is right? Sadly, neither of them. Even the question is wrong. Most men today actually wear the popular boxer-brief hybrid known as boxer-briefs. Briefs (eg Y-fronts) have long suffered from a reputation as a juvenile, comical and sexually unattractive undergarment whose snugness presents a threat to the wearer's sperm count. Boxers, therefore, used to be the obvious right answer, but walking around in them all day was another matter. To this dilemma, boxer-briefs offered the perfect solution: pleasingly restraining, but it wasn't the end of the world if the au pair saw you in them.
Perhaps in Bill Clinton's day this question held some vestige of meaning, when men were still lining up on one side of the divide or the other and demanding to be counted. But today we all wear boxer-briefs: every single one of us. Cameron and Davis were probably wearing them on Woman's Hour, but didn't know what they were called.
There is another matter to ponder, which is whether we have reached the low-water mark of political debate when candidates are routinely required to field questions about their smalls. The answer is no: that will probably happen some time next year, when Tony Blair decides to tell June Sarpong that most days he prefers to go commando.
