That $nick should be $$1. $chan can be # for short.
It\'s kinda late.

Yours would be nice if their versions didn\'t support the \"-k\" switch I\'d also suggest using:

kickban {
var %kbnick = $$1, %kbreason = $2-
ban %kbnick 3 | kick # %kbnick %kbreason
}

That way you don\'t need to unset the vars.