instead of doing

if ($3 != n00b) && ($3 != loser) && ($3 != fail) && ($3 != leech)

you could use $istok

!$istok(n00b|loser|fail|leech,$3,124)

and look into useing $iif
also you may want to check if $2 is in the channel

on *:TEXT:!label*:#:{
  if (!$($+(%,lbl),2)) {
    set -u3 $+(%,lbl) on
    if (!$2 || $2 !ison # || !$3 || !$istok(n00b|loser|fail|leech,$3,124)) { .notice $nick $iif(!$2,No nick was entered,$iif($2 !ison #,Sorry Can't Seem To Find $2,$iif(!$3, No label was entered,$iif(!$istok(n00b|loser|fail|leech,$3,124),$+(,$chr(40),$3,$chr(41),) Is an incorrect label!)))) }
    else { msg # $nick has labeled $2 a $+($3,!) }
  }
}