elseif ($nick != nick)
{ msg $chan Different message for this specific person here }
}
change the ref object ("nick" in this case) to the persons actual user name and it should work.
Example:
elseif ($nick != majeye)
{ msg $chan Majeye is one heck of a guy! }
}
This should yield:
"Majeye is one heck of a cool guy" upon entering your chat, or in response to a specific word I typed, or however you set it up initially, and would only work for me since you specified 'majeye' as the reference object.