Pretty simple really. You answer the word in the post above you with "is not relevant to" and then answer it with something else. Then either you use that word or a different relevant word relevant to your answer and... it starts all over again as someone else answers you and repeats the process...
Can be a single word or a subject, noun, verb...be creative but don't overdo it.
If the post above you screws up, you may merely point it out or make light of it... or simply quote them and give them one of these:
I would encourage you to say "Fail, GTFO." except I'm afraid you might get infracted and I will get infracted for every time you do it thereafter. Oh wai...
On occasion you can quote someone else and make a wisecrack or whatever.
EDIT: I guess it begs an example....
"Dumpster diving" (quotations not necessary)
is not relevant to headbanging
(inclusion of previous post's term not necessary)
Then you go on to restate
your term or something relevant to your term
I.E. this case headbanging, or similarly mosh pitting
or maybe crowd whirlpools
is not relevant to KOTOR MODDING
(and so-on and so-forth)