A dumb-assed replacement phrase for the word-phrase "comeback", which, in normal people English, means "retort".
It makes no sense since "clap" is a word that doesn't represent anything having to do with the meaning of the intention behind the phrase, and meaning something completely different.
In fact, you could replace the verb aspect of this word-phrase with almost any verb, such as:

Fartback
Pushback
Suckback
Blowback
Pickleback
Sayback

and the dumb-assedness of the phrase stays the same, since the focus isn't on it's etymology, but the intention of meaning that the speaker has. The reason that this is dumb is because words mean things and, now, we're arriving at a place where any word can mean anything. This, of course, will inevitably lead to the world simply "barking" at each other like dogs would since, in the future, all we'll need to do is make noises at each other to get our points across since no specific word holds any intrinsic meaning anymore.

A celebrity free pass is an agreement between you and your significant other that if you meet said celebrity and there is an opportunity to sleep with them, your partner cannot get mad at you for doing so because you had agreed before hand that this person was your celebrity free pass. It is ideal if both of you in the relationship choose a celebrity free pass so that the playing field is even.

basically a comeback, most likely pumped with attitude, sass and or shade.

to return fire.

To respond to an insult by answering while clapping your hands in rhythm of your words, in order to add empahasis. Common among outraged ghetto women...

To return a diss, particularly one related to a beef in the hip-hop world.

-to insult someone after they insult you