When Barney enters the booth and says "No two single people in the world are ever platonic" and then pauses before saying "Symposium," he is making a subtle reference to the Greek philosopher Plato and one of his most influential works, 'Symposium'.
The lens skyscraper built by Hammond Druthers was inspired in the 20 Fenchurch Street "Walkie-Talker" solar glare problem (London City, previous -2013- summer).
While Robin is telling the redhead at the bar that she is Ryan Gosling's personal assistant, Marshall is at a basketball game where he announces that Ted is Nicholas Sparks, prompting one of the coaches to admit he loves 'The Notebook'. Ryan Gosling stars in the movie adaptation of Nicholas Sparks' 'The Notebook'.