"The robot falls in love"
I rewatched Season 2 Episode 16, "Stuff," and I just realized that this, like many other moments in the first three seasons, is a comedic moment that actually very subtly foreshadows Barney's future with romance.
Barney is like a robot in his apparent beliefs about romance and sentimentality, but he starts feeling these things himself, and specifically with Robin, he struggles to compute or reconcile them with the way he thinks he needs to be. "Feelings inside! Oh no!"
In the second robot scene, instead of speaking robotically, he's actually singing, and about "the One," no less. Not only is this amazing foreshadowing, but it hints at Barney's buried romantic desires; why else would he depict himself this way in a play he performs just to prove a point to Lily?
The show may not have ended perfectly, but its foreshadowing and continuity are unparalleled!