Erm.... don't say it 'nicely.'
Point blank say 'I'm not interested, please stop harrassing me, you are making me very uncomfortable and if this continues I will have to take it up with the senior people within this company'
Stop being so b100dy nice about it, he's becoming an irritant... if you spilt bleach on your skin you'd be pretty quick with washing it off right before it burns?!
Honestly lady, I'm not kidding, he's not responding to 'nice,' tell him to bog off and get a life.... (but use my other sentance ^^^^ and not that one)