I would do a little different:

The first line (where nick1...nick3 is) can be a list of people you don't want to greet, space delimited
the second is a list of excluded channels, space delimited
the third, (where GREETHERE is) will be the greet message.

The timer is named based on nick so that if two people join in a row they both get greeted, but if the same person joins and parts and joins... they don't unless it's after three seconds.

and finally, I would put something like "Welcome to $chan, $nick $+ !" for my greet, so if bob joins #joe, it will read "Welcome to #joe, bob!"

alias -l bad { return nick1 nick2 nick3 }
alias -l cbad { return #chan1 #chan2 #chan3 }
alias -l greet { return GREET HERE }
on !*:JOIN:#:{
  if (!$istok($bad,$nick,32)) && (!$istok($cbad,$chan,32)) {
    .timer $+ $nick 1 3 msg $chan $greet
  }
}