Chandler: That's it? It's over? Who shot J.R.? Who shot J.R.?!
"Who Shot J.R.?" is a reference to the TV show Dallas, where the character J.R. Ewing gets shot in the last scene of the last episode in Season 2. During the wait for Season 3, "Who Shot J.R.?" became one of the most famous TV series cliffhangers ever.