What you may not recall is that the fellow doing the proposing mentions that they'd had their first kiss at the party for the show's 100th episode.
It was the ending of that 100th episode that I'd bee searching YouTube for!
So, I might as well post it.
It requires a little background. And know that it won't be nearly as impactful as if you'd seen the whole episode, which was really clever and wonderful and emotional.
The episode was an homage to The Wizard of Oz, called "My Way Home." In it, resident doctor J.D. (played by Zach Braff) is on a day off but called to he hospital, much against his wishes. But he gets involved in a range of stories that keep him from being able to leave and get back home. As the episodes nears its end, we get the resolution of three of the main storylines --
Turk has avoiding telling the parents of a patient in a coma that their only real choice is to pull the plug, because he wants a heart to perform the hospital's first transplant. But in a very moving scene he finally faces the family about the medical reality that's really their only option, saying goodbye to their child, and understands that he doesn't need someone else's heart.
Dr. Elliot has been impressing her class of interns by seeming to be an expert on endocrinology, when in fact she's been hiding crib notes all around the hospital so she can answer questions. A lecture is coming up however where that won't be possible, and she's completely freaked-out, but is at last convinced to rely on her brains and cram to remind herself of all the information she really and proudly does know.
And prospective mother Carla, a nurse, is terrified about becoming a parent when she's put in charge of taking care of the little son of one of the doctor's for the day and can't handle it and so find every excuse to avoid all responsibility-- until she ultimately gets the courage to face not only the child with her, but the joyful prospect of her own.
It's also worth noting that throughout the series, Dr. Cox continually insults the wimpy J.D. with girl's names. (You may recall in that proposal video he refers to J.D. as "Sharon.") But the name he most often uses throughout the series is -- Dorothy.
And so here, then, is the final scene, with the resolution to all the stories. At the top of the building is lawyer Ted with his recurring a capella singing group. And it's worth noting that Zach Braff (in ruby red shoes throughout) directed the episode -- with this lovely, and intricately-timed last sequence..