I start: I do this all the time, and with most cases I can end up to somekind of conversation. You just have to be polite and smile. I am also in happy position because my wife knows
about this fetish and (yes!) wears big mens watches I have collected (Rolex, TAG, Omega....) Also in bed. 
I can even say to her that "Sorry honey, I missed what you said. Can you repeat? I was drooling that huge diver watch that girl is wearing. Can you see it?" 
and she hits me with her purse or something. Heh. Live is soooo good.But before I had nerves to do this I found easy place to practise. (And still do it when having time to kill in airports or so.) Go to jewellery. Say hello. Be polite and smile. Say that you are looking for watch to your wife/girlfriend and what kind of watch you are after. (In my story my wife dives, likes big watches and/or coaches kids foodball so she wants chronograph watch.
) Then do following and see how far you have nerves to go:-Check what kind of watch she is wearing: if its nice say "I'm looking for something like that. Wow. Its nice. Do you have something similar?"
-"Actually yours is pretty nice. Can I see it."
-Ask her to show some models
-Ask her to try some it to see how it fits. (To check if its too big. Funny that they never are.)
And remember that gentleman is always ready to hold her watch when she removes it...-Say "Wow! it really looks good on your wrist" Have you ever though to buy that watch? You should. Its looks great on you!"
-Ask to snap a shot about her wrist with your mobile. "To show picture to my wife about model." With some luck you end up having pic with two watches: model you are looking and her own piece.
Feel free to try and share with us.
