When you have a nick: if ($me == YourNick) { do stuff }

if someone else need to have a nick you want to trigger on:

if ($nick == UsersNick) { do stuff }

Code:
on *:text:Coffee:*: {
   if ($me == YourNick) { msg $chan $read(C:\Program Files\mIRC\coffee.txt) }
}

on *:text:Coffee:*: {
   if ($nick == UsersNick) { msg $chan $read(C:\Program Files\mIRC\coffee.txt) }
}