So may I ask if asking for a kiss (albeit once or persistently) isn't harrassment in your eyes....where does harassment start? A few slaps of the bum? A hand up the skirt? Unzipping the back of her dress?....and so on...
The last bloke to try one of the above (on this occassion hand up skirt) on me got a 6 inch stiletto slammed down onto his foot, didn't look quite the Romeo infront of his mates then.
Harassment is doing something that makes someone else feel uncomfortable, where that uncomfortable level is depends on the person. The safest solution is to not act like an out dated sexist pig and keep your hands/ideas to yourself, this isn't the 70's. The way you describe is that he 'innocently' asked just the once, I take from the OP she's sick of constantly being hit on by her staff....slight difference in scenarios I feel.