Furiny, can you clarify whether you have a specific word in mind, or just that several people say the same thing in close proximity, whatever that is.
G16's code works for a specific word being used within someone's sentence, but it works on the 4th occurrence, but it also keeps a permanent count for all time, using the very common %i variable that most scripts feel free to use. Better to use something like %scriptname.i instead. Also, if you want to count people doing it only within a few seconds of each other instead of counting someone doing it across several days, change
to instead be:
inc -u5 %i
The -u switch unsets the variable after 5 seconds delay, so as soon as someone does not use the word for 5 seconds the variable vanishes regardless of the value, but each time someone uses the magic word the countdown resets to 5.