I met someone at work a few months back. He works in a different department, but often comes around to chat with people. He’s been talking to me a lot, trying to get to know me, and I’ve noticed he seems different to me than to other girls. He talks about personal things sometimes, and lately has been saying some sexual/perverted things. Also, whenever he sees me or talks to me, he brushes his hand against my arm or nudges me.
There are times, however, when he ignores me — when he’s with other people (male or female), sometimes he pretends I’m not there and pretends he isn’t looking at me. I haven’t known him for that long, but it really confuses me, because it would seem as though he likes me, or at least wants to have sex with me. But then there are moments when he acts like he has a problem with me.
He teases often in a friendly way, but sometimes he is just mean, and I really don’t know what to think about it. Somebody said it might just be that he wants to have sex, but doesn’t want to tell me, as it might be inappropriate. I’m not sure what to believe.
LemonVibe 
You are being sexually harrassed. I would document each and every time he does it and speak to your boss and hr.
run the other way. not a good sign at all.
As a woman, I do this kind of stuff ALL the time when I like people. I don’t really know why, I think it’s mostly just a tactic to let the person know I am interested but not too interested.
However, (not to seem sexist) since he is a male and this is in a work environment setting, I would probably be a little leery about the situation as well. Maybe try to talk to him about it in private so you can understand exactly how he feels about you, and don’t settle for a wishy washy answer. If you start to get an uncomfortable vibe from the situation, don’t hesitate to report to HR.
Hes just a fuckboy. Move along.
It’s not what I think, it’s what I know. The coworker you write about is a very smooth operator, used to seducing women quite easily. His tactics are perfect, the hot/cold approach. He sexualizes your thoughts of him while at the same time sending you the impression that he doesn’t care about you at all. That would WORK on most women (especially young ones).
I can tell you exactly what he wants, and I am not guessing here. He wants to have sex with you. NOTE that he does not want you to be a girlfriend, he just wants to use you for sex.
Now, what should you do about it? Well first of all, never have sex with him. That is, unless you are not working with him anymore and you are OK with the fact that the sex will be just sex and nothing else…