Well, this is an interesting idea. I'd probably give the bartender an ACTION type trigger, triggering on *, with NArg 1.
Such a trigger will fire on any input, particularly fight messages.
So, when the trigger fires, we need to determine if the one triggering the script is fighting (after all, other messages trigger an action trigger as well - like enter and leave).
This can be checked with "if %actor.fighting%". If that is the case, just "say No fighting!" - no need to force a mob to do something itself.
Now, to prevent the trigger from being triggered over and over again, you can simply add a sleep time after saying the sentence. A trigger that is already running will not be started again.
The last thing to do is to add an end to the if statement.
So you'll end up with someting like this:
Code:
if %actor.fighting%
say No fighting!
wait 120 s
end