This just-posted video has already scored over two million views... we'll let it tell the story:
Staged by 'Improv Everywhere', here is what the YouTube video description says about it:
"For our latest mission we recreated the famous fake orgasm scene from When Harry Met Sally with actors dressed as Harry and Sally and 20 additional couples in Katz's Deli. When Sally's fake orgasm began, 20 additional women (on dates with 20 men) joined in one by one, creating an over-the-top surprise for the Katz's employees and patrons. This was staged without the knowledge of the restaurant, though thankfully they all seemed to love it."