@jbl09,
If it's at work, get it on video if you can, get your coworkers to agree that they saw it and write a quick statement, then take it to HR. If HR won't back you up, go to the level of management above HR. If you're still not getting anywhere, get a labor lawyer. Or, if you don't want to deal with all that, change jobs (preferably to somewhere with less feisty female colleagues). The woman behaves the way she behaves because she thinks the system will back her up -- the key to combating someone who is leveraging the system against you is to either leverage it back better, or leave.
If it's your own woman, if you know she cheated, give her the boot. Or deal with it however you need to deal with it... I know some guys don't have infidelity as a total deal breaker, so if not, then demand whatever concessions you require of her to call it even. Tell her she owes you four FMF threesomes over the next three months to keep the relationship, or what have you.
If she is crying, lying, complaining, but you know it is bullshit, dismiss it, grill her, tell her you know it's bullshit, get her to admit it is -- do whatever you've got to do to satisfy yourself.
Some women will never admit you caught them in a lie. Some honestly don't believe they are lying. Many will put all kinds of spin on things even if they admit they didn't tell you the whole truth. You are not going to always (or even often) be able to get a woman to deal with you with male levels of honesty/objective truth. But you do need to be able to interrogate the truth out of people, if you want certainty instead of just to hang around in doubt.
e.g.,
Her: I went over to John's place and he raped me!
You: [immediately skeptical] Why were you over at his place?
Her: It was for work! Our boss said we had to work on the project together!
You: He did? Do you have a message from your boss I can see?
Her: No. He said it when we were at work.
You: All right, I'm going to talk to your boss later. How did this rape happen?
Her: We were blah blah blah and then he said we should sit on the couch, so I said okay. Then blah blah and he started kissing me and I told him no and blah blah and then he blah blah and then he raped me!
You: Did he bruise you? How did you fight back? Let me see your injuries.
Her: I didn't fight back! I was afraid he'd hurt me!
You: How did he enter you? I've tried to shag girlfriends a hundred times when they were unwilling and never got it in after hours of trying.
Her: You think I'm lying?! blah blah!
You: I'll talk to your boss tomorrow, but this smells like bullshit to me.
Her: Fine. John got me really drunk and blah blah but it was still rape!
You: Yeah, I didn't think it was rape.
Her: He did not have my consent!
You: Get out of here with that nonsense. I've been drunk a million times. Never once have I done something I didn't WANT to do. Nor has anyone ever forced me to drink. You're full of it.
Her: [SOB!]
You: Get out. Go back to his place.
Her: [SOB!]
You need to already be in a certain mental place to interrogate a 'victimized' woman like this.
The first is that you do not 'believe all women', but rather make quick judgments based upon your read of a situation.
If a woman steps into my apartment with a black eye and a bloody lip and her clothes slashed and torn and says she was raped, I'll be inclined to believe her from the start (but I will still interrogate her -- albeit gentler than in the example above).
If, however, she comes in looking all nice and pretty and fine, with no bruises, then starts pulling out a sob story about how her nice colleague whom she has mentioned several times and whom I suspect she has a crush on 'raped' her, it's going to smell very fishy to me.
If you want to avoid a full interrogation of the woman, you can also just tell her to give you the man's contact info, because you want to talk to him and get his side of the story. If it's a false accusation, she is going to panic over this, because she doesn't want you and him comparing notes on what she's saying. The whole ruse breaks down if the distrust between the opposing males is broken down and communication lines open up. You should also be trying to talk to her boss, her friend, any other involved parties that were aware of some aspect of the situation to get their side of how things went down. Again, the more defensive she is of not letting you talk to these people, the more suspicious you should be.
A woman who was genuinely assaulted will be shell shocked, and should be willing to go along with whatever her defender proposes to do.
It's not a smoking gun if she is resistant to you talking to people, but it
should raise your suspicions further.
No one is going to hold your woman to account if you don't.
The rape example is an extreme one, but every man ought to be able to interrogate women for truth on issues where the truth is important to him.
Chase