If those suggestions don't work, then try looking him directly in the eye, and give him the biggest baddest stink eye that you can give, and you know us women we have the look of stink eye down to fabulous art. Then say, "Are you for real?" roll your eyes and just walk off.
That's very true! I've seen many a man be stinkeye'd even from accross the room it sends their heads turning and egos shot down. lol I think some women have laser beams in their eyes so when they do the stink eye it shoots an invisible ray. 
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Seriously though, go the HR route that others have suggested. Tell him that if he makes any further advances, you'll contact HR regarding harassment. Keep it polite, firm, and clear. As for the girlfriend, if you don't know her well, let karma take care of it for him.
