You can see from the pictures that these girls were making quite a thing of fluffing up their hair, adjusting their make-up etc before taking a shot of themselves. I would imagine that the resulting pictures they took ended up on Facebook.
"Us on the Tube getting ready for a gr8 nite out LOL!" as a possible caption.
Thanks to astromatt76 for being so observant although from the reflection in the window I bet the rest of the carriage were watching in amusement too.