This one is not actually a universal rule. True, someone locked in a steamer cabinet can have a certain comic appeal, but is it always funny? The current rarity of steamer cabinets in comedy has made this particular rule a bit passe. So, while the other two rules are universal and immutable, this rule can be pretty much disregarded. Then why have this rule on the list, you ask? Simply because there must always be a third rule. Comedy is based on series of three. For example, Who's on First, What's on Second, I Don't Know's on Third Base. My Three Sons. The Three Stooges. I could go on, but I've given three examples and any more wouldn't be as funny.
There was a time where Derek contemplated replacing steamer cabinets with Russian Squat Dancing. True, this particular style of dancing can be used to comedic effect (see, for example, that Disney film about the wooden boy with the long nose), but is it always funny? Or is there perhaps some other staple of comedy that is always funny but not on this list? There is so much we just don't know.