kick # $nick your kick message here
Btw, the mIRC helpfile has good information on most available features in mIRC.
Might be a good idea to type /help when you're wondering about something. It's a good way to independently seek for information, and to use it accordingly. Personally, when I'm curious of how something worx in mIRC I either check the help file, or the Search
feature of this message board.