Mine

on *:JOIN:#:{ if ($chan != #mirc) {
    inc %joins [ $+ [ $nick ] ] 
    timer 1 15 unset %join [ $+ [ $nick ] ]
    if (%joins > 3) { 
      kick $chan $nick 
    } 
    if (%joins >= 5) {
      ban -k $chan $nick 
    } 
  }
}