For me, it adds a little extra something to a story, and when I stop to consider why, I think it's because it shows that the author is thinking about her world as an entity that lives apart from the story you see "on screen." And besides, it's just plain fun.
In Firelight, my small contribution is Cheese on Toast, also known as Welsh Rarebit -NOT to be confused with "rabbit" as I often did as a child.
What is Rarebit? Basically, it is a melted cheese sauce over toast. But this Wiki article explains it quite well, if you've a hankering to know all there is to know about the dish.
Now as to my purposes, it's also a well-known pub dish in the Victorian era in which my story revolves, and more importantly, it's melted. Why is that important? Because my main character Miranda can, if prompted, melt things quite well. And this is the only rule when inserting a running gag: it has to work within the world and the story. Too random, and it's obvious. You don't want obvious -at least at first.
Using the chicken shirt in Roseanne as an example, if they say, wore a diamond tiara instead, the joke would fall flat because it wouldn't be something to catch, but rather a bit of silliness that distracts the audience.
Here is the scene in which Cheese on Toast first makes an appearance in Firelight.
"Leave off," she said with iron in her small voice.
The street ruffs laughed, an ugly sneering sound. "Oh right, leave off, she says."
The taller one snorted. "Listen 'ere, toffer, behave an' we'll leave you intact."
Green eyes blazed beneath her auburn brows that arched like angel's wings.
They were green, weren't they? Archer squinted, his abnormal eyes using what little light there was to see. Yes, crystalline green ringed with emerald, like the cross section of a Chardonnay grape. Yet he swore he saw a glint of orange fire flash in them.
"Leave now," she demanded, unmoved, "or I'll turn you both to cheese on toast."
Archer could not help it, mirth bubbled up within, and he found himself laughing. The sound echoed off the cold stone houses and brick-lined alley. The young men whirled round. The fear in their faces was clear. They weren't up for an exchange with a grown man, most especially any man who'd be out on the streets at this hour. Archer knew their cut, cowards who preyed on the weak and fled at the first sign of true danger. He came close enough for them to see his shape and the toes of his Hessians, preferring to stay in shadow until necessary. END
Running gags are just as fun for the author to use as they are for the reader to find. Perhaps you might like to try? :)
And if all this talk of cheese on toast has put you in the mood to try some, here is a simple recipe brought to you by good old Alton Brown at the Food Network, as well as a bit of video entertainment by way of the Two Fat Ladies.
I don't know if you've ever seen the ladies, but they crack me up, and seem so quintessentially British baking mama to me. This is actually a two for one deal since they are also making chocolate creme brulee (yum!)
I don't know about you all, but I'm hungry!