If you're saying you don't understand what slacker did, Aucun,

on *:action:$($+(*,pets,*,$me,*)):#: { if (!%purrflood) { set -u3 %purrflood on | .timer.purr 1 1 describe # purrrrrr.... purrrrrr.... } }

There is a $ infront of the $+(,pets,,$me,) because you cannot directly use identifiers like $+'s as a match.
is just a wildcard, so there can be anything between "pets" and "$me".
So the script can be activated, assuming let's say the bot nick is CatBot, by saying something like:

/me pets the bot CatBot by touching her fur.