Ok, thats simple enough.
Just put the code in an event.

Code:
on *:TEXT:!slap-all:#channel-name:{
  var %nr_of_nicks = $nick($chan,0)
  var %total_nicks_that_will_be_slapped = $calc(%nr_of_nicks - 1)
  if (%total_nicks_that_will_be_slapped == 0) { echo 4 -a = $+ $time $+ = Dude, there is nobody to slap except yourself :/ }
  else {
    var %i = 1
    while (%i <= %nr_of_nicks) {
      var %nick_temp = $nick($chan,%i)
      if (%nick_temp == $me) { inc %i }
      else {
        var %nicks_slapped = $calc(%nicks_slapped + 1)
    var %nicks_to_slap %nicks_to_slap $+ %nick_temp $+ $iif(%nicks_slapped != %total_nicks_that_will_be_slapped, $Chr(44), $Chr(46)) | inc %i } }
    describe $chan spanks the shit out of %nicks_to_slap 8Time to wake up!!!!!!!!
  }
}


Do !slap-all from #channel-name