There is this creepy guy in the office I work at - he always checks me out in a really obvious way and doesn't even try to hide it when I look at him! He is so unattractive by the way lol. He says hi and I just try to act cold, (I say hi and keep going back to what I am doing without making too much eye contact). He still doesn't get that I am not interested lol and just keeps doing it every time he sees me. I can't just ignore him when he says hi cos then I will look like a bitch - and unprofessional to anyone else who sees me so I have to at least respond. How do I handle this situation?