One timeless sitcom classic is of course the ubiquitous "locked in the room" situation.
Two characters who have probably not gotten along well in previous episodes will suddenly find themselves locked together in a bank vault, large freezer, or in the case of "Valerie's Family" painted into a corner, waiting for it to dry. At the end of the episode the characters have told things to eachother that they have never told anybody else, and have learned that they are really not so bad. In the next episode they go back to disliking eachother once again.
What's funny about this is that my sister worked at a McDonald's a few years ago and her, along with every other new employee was deathly afraid of locking themselves in the freezer and would go to great lengths to have the door held open for them while they were in there. When in reality there was a handle on the inside of the freezer to prevent anybody from being locked in. Just like every other walk-in freezer ever made.
This is not directly related to the very special episode of Punky Brewster where one of the kids locks themselves in an old refrigerator and passes out from lack of oxygen.