1) On the street:
Ignore it. It's tempting to say something back to a guy who's hollering at you, especially if he's being disgusting about it, but if you talk to him you're giving him exactly what he wants: your attention. (This also goes for "nice" guys who direct you to smile or tell you you're pretty — they're usually harmless but are annoying anyway, and you don't owe them anything.) If you absolutely can't resist responding, though, keep your cool. Without smiling, look directly at him and say in a neutral tone, "Repeat what you just said to me." Most of the time he'll realize how stupid he sounds and will be tongue-tied and sheepish. (Alternately, call him out on it by snapping his photo with your cell — then send it to street harassment blog HollaBack). Occasionally a guy will get defensive and say something rude back to you, like calling you a bitch or saying something mean about your race or appearance. That's just his way of trying to get you to talk even more with him. Don't fall for it; just walk away.
2) On the job:
If a coworker is making you uncomfortable, talk to your manager. It can be helpful to make it clear to your coworker that you're not interested in playing along — as in, no flirting with him. But even if you were flirting with him once upon a time and then change your mind about how you feel and he keeps going at it, that's not cool — and it needs to stop. Sometimes girls worry about getting a guy in trouble if they "tell" on him, but remember that he's the one acting inappropriately, not you. If it turns out to be a case of him honestly misreading your signals and he lays off, then you can happily report to your manager that he stopped bugging you. (He doesn't have to want to make you uncomfortable to do exactly that; "nice guys" aren't exempt.) You have the right to do your job without the burden of dealing with a guy who makes you feel weird.
What if it's your manager who's up in your business? Talk to that person's manager or human resources ASAP. The longer you ignore it, the worse you'll feel. If you have a hard time getting the words out, try asking your boss's boss, "What's the company's sexual harassment policy?" That can open a dialogue about what you've been experiencing.
3) On your own time:
If a guy asks you out and you're just not interested, being firm but clear will hopefully take care of it (as in, "I'm sorry, but I'm not really feeling it"). If he persists, don't be afraid to be more direct. It can be hard to say things like, "Please stop calling me," but some guys are programmed to think that they shouldn't take no for an answer. It shouldn't have to be your responsibility to tell them that no means no (how hard is it to understand?), but it unfortunately becomes your responsibility in that moment if you want it to stop. Their feelings may be hurt for a bit, sure, but they're hurting you by repeatedly bugging you.
What to do when the situation is more aggressive — like, a guy at a party touches you in a way that icks you out? Your first responsibility is to make sure you feel as safe as you can. Get up and walk away, grab a friend — whatever will help you feel okay. If you feel like confronting him, try something straightforward like, "Why did you put your hand there?" It might feel embarrassing to call attention to it at all, but remember that he's the one who should be embarrassed by what he's doing, not you.
