%tmpslp = $replace($read(slaps.txt),<m>,$me)
  %tmpslp = $replace(%tmpslp,<u>,$nick)

could be
%tmpslp = $replace(%tmpslp,,$nick,,$me)
and
unset %tmpslp
isnt needed, it is needed when you set variable with /set, this time it isnt setted. (after script using it will automatically delete)