What do you call a word that follows a punchline or a practical joke and is used to emphasize it?

Popular culture often has people use a specific kind of word to capitalize on a joke they've just told, or a prank they've pulled on someone.

Examples of such exclamations would include hey-oh that might follow an especially raunchy joke:

I got a powerful urge to help you out

So what's your wish? I really wanna know

You got a list that's three miles long, no doubt

Well, all you gotta do is rub like so (rubs his buttocks) HEY-O!

(Disney's Aladdin - Friend like me)

... bazinga, coined by the Big Bang Theory show:

You actually had it right in the first place. Once again, you've fallen for one of my classic pranks. Bazinga!

Similarly, there are more aggressive exclamations such as "Boom!", "Bam!", "Bang!" etc. that are sometimes used to double down on a hostile statement or action, and are meant to cause additional embarrassment and pain.

Is there a single word used to describe such "punch line markers".

I've already thought of "slam", "burn", "exclamation", "interjection", and "catchphrase", but they're either too generic, or don't work in all scenarios.

Solution 1:

The following interjections are onomatopoeic, imitating the sound of the drum sometimes followed by the crash cymbal.

• ba-dum dum
• ba-dum tish
• ba-dum ching
• ba dum tiss

In the early 1970s, a British fox puppet named Basil Brush, popularised the catchphrase “boom-boom!”, which was the signal for children watching at home to laugh because the TV puppet had told a bad joke, often in the form of a cringeworthy pun.

Some comedian writers call these type of expressions a punchline indicator

Any of three words in bold would describe the phenomena in the OP's question.

Solution 2:

In performance such words following the punchline make the Applause Line or Applause Cue. As stated this tells the audience when they can laugh by letting them know there are no more lines for that joke. These are invaluable in managing the audience's attention. Pre-built lines, Bazinga for one, belonging to a character gives them great power to change the story and control reactions.

Most often such cues are quiet and subtle, designed to pace the story by allowing tension to build and release in a known pattern for both comedy and drama. Overemphasizing the punchline or the Applause Cue out of all proportion is know as Hitting it Over the Head and spoils or displaces the enjoyment of even the crudest of humor. In some shows it is that heavy handedness itself that is the entertainment. Long live Svengoolie.