How would you reason with a JW that is okay to say Good Luck?
We can start by showing them what their own literature says.
(W 9-1-1980 QFR p30, par4) "Gamblers often magnify 'Lady Luck.' For them "luck" is not a word merely meaning good results, but is a superhuman influence like a god. Greed and pride move gamblers to trust in "luck."" (bold added)
It
seems that saying 'luck' to simply mean good results is alright, but to
rely on the God of Good Luck in serious ways, such as gambling, is off
limits.
I don't know if Watchtower actually taught at one time
that saying 'luck' in any fashion was bad because it was pagan, and
later backed up on that, or if it was simply a myth that arose among
Witnesses to begin with.
At any rate, when we say 'good luck' to someone, or 'wasn't I lucky because I found a dollar,' we simply mean
good results.