Answer - When it's shorts.
A visiting American golfer was banned from playing Royal Troon in Ayrshire because he was wearing a kilt. Dr Jeffrey Foster, who is of Scots descent, played rounds at seven other championship courses, including Muirfield, Turnberry and St Andrews, without any problem with his attire, yet when he arrived at Royal Troon, he was told he would have to change into trousers to tee off.
Dr Foster said: "As a 13th-generation Scots-American I own 14 traditional kilts and often play golf here and in the US kilted. I intended playing every round in Scotland kilted, in honour of my heritage and homeland. I showed up properly kilted and was denied permission to play at a pre-arranged and pre-paid tee-time because there is a rule against men playing in shorts. The official record at Royal Troon equated my kilt to shorts." The American reluctantly dashed back to his hotel to change into trousers.
The club's information for visitors on its website states only that 'denim jeans, shorts, tee-shirts and training/sports shoes are not permitted in the clubhouse or on the courses'. Royal Troon needs to revise its website because it wasn't long ago I was at a function in that clubhouse and most of the male guests were kilted and none was asked to leave or change into trousers. I'll be delighted to furnish them with the date if they so wish and I'm sure I can dig out a few photographs for free.