See those two elderly men, sitting outside the cafe, holding hands?
Yup, those are future!Klaine.
The one with the red cardigan is Blaine, of course. The one sitting crossed-legged is Kurt.
They used Brittany’s time machine to see themselves a day before everything changed - before Blaine transferred, and their relationship became so much more - stronger, wiser, better: much more than just some high-school sweethearts.
They’re talking about themselves, in this scene. Blaine is smirking and commenting something about how he loved getting to see Kurt in regular clothes everyday - especially the skintight jeans. Kurt is rolling his eyes at him but smiling, squeezing his hand.
And you simply can not convince me otherwise.