So that's what the title meant. It wasn't an allusion to Clara's last Christmas (more on that later) or the Doctor's last Christmas or not even that much anticipated Wham! crossover that everyone was secretly hoping for. It was actually a reference to the fact that every Christmas is someone's last Christmas, which is actually quite morbid if you think about it. It's a heartwarming sentiment nonetheless, however, or at least one of those Steven Moffat sort of heartwarming sentiments which warm the cockles of your heart but leave you questioning the morals of humanity in the process. Isn't that what Christmas is all about? Fundamentally it's a reminder to always make the most of the time you get with your loved ones and for Clara Oswald and Danny Pink, that time has unfortunately ran out. Let's not get ahead of ourselves, though. But seriously. No Wham!?