Q:

What is the recourse for defamation?

I came across this question today https://interpersonal.stackexchange.com/questions/23296/i-was-mistakenly-identified-as-a-criminal-and-this-has-caused-rumors-how-can-i and I think OP is taking the issue way too lightly.
What kind of recourse can OP pursue to swiftly clear their name? Do they have a strong case for egregious defamation?

Full story below in case the IPS link goes bad in the future:

A while ago, I was at a popular, busy local nightclub (this is in the Unites States) and ran into a friend of a friend. Let's call her Anne. After a bit of conversation with Anne, and mutual name-dropping of our overlapping social networks, a bouncer approached me and said that he was asked to escort me off the premises. I had no idea why, and the bouncer said he did not know either, only that I had to leave immediately. I know enough not to argue when the door staff have made up their mind, so I agreed to leave without complaint.
I assumed it was because maybe I looked a little intoxicated-- I wasn't really, I had 2.5 drinks over 2 hours-- and thought nothing more of it.
A week later, a different friend contacted me and informed me that I had been 86'd from the club because I am a "known sex offender." After I had been escorted out, the bouncer had told Anne this. Anne, by the way, volunteers as a rape counselor and is a strong and feminist advocate for social justice. Over the past week she had defriended me on social networks and starting contacting our mutual friends to inform them of this "fact" out of concern. Because I am defriended I cannot see what she is saying about me nor can I respond. I only heard about this from a friend of a friend of a friend.
This is a clear case of mistaken identity. I hadn't been in that club in more than five years, so there was no way I was a person that would have been known to them. I have done a search of the local sex offenders registry and I am not in it. I have never been arrested, let alone indicted of a crime.
I am obviously devastated by this and very depressed. I am not sure what to do about it. My friend suggested I go back to the club and confront the manager, but my feeling is that in a situation like that the manager has to side with their employees.
I considered reaching out directly to Anne, but my gut tells me, given the situation, that she would interpret this as a form of intimidation and it would simply make things worse.
What can I do to fix this situation? My goal is to quash the rumors and cleanse my reputation in my social circle.

A:

Scott seemingly has a viable claim of defamation per se. If the matter has caused him concrete losses (typically in the form of losing employment, business, or prospect thereof), he could also sue for defamation per quod.
The matter of defamation per se will require him to prove the defendant's mental state known in defamation law as actual malice. That term refers to defendant's knowledge --at the time of making the statements-- that the statements were false or defendant's reckless disregard of the truth or falsity of the defamatory falsehoods.
During the discovery stage of the judicial proceedings, Scott might be able to ascertain the source of the defamatory falsehoods. That will be crucial toward proving the defendants' role and mental state regarding the false accusations.
Being a mental state, actual malice is somewhat difficult to prove. Scott gives no information --and apparently has none-- about the alleged source of the bouncer's "knowledge". For instance, he might just have followed instructions from his employer, who in turn would be another defendant to the lawsuit.
As for Anne, her reckless disregard of the truth (and hence actual malice) might be easier to prove. She as "rape counselor" is expected to have undergone some training, and thus be aware --as all of us are-- that many accusations of sexual misconduct are false. Thus, she will have a harder time explaining why despite her alleged profile of "rape counselor" she rushed to spread the falsehoods.

Because I am defriended I cannot see what she is saying about me nor can I respond.

Before she removes her posts, Scott should ask mutual friends to save copies or take screenshots of what she has been posting about him. That evidence is important even if Scott eventually subpoenaes the social networks where Anne is defaming Scott.
The statute of limitations for claims of defamation is one year --from the time of publication of a defamatory falsehood-- in most of the U.S. An exception is Tennessee, where it is only six months. Scott will be able to sue only for publications/statements being made less than a year (or six months, accordingly) ago. This is noteworthy because Scott begins his inquiry with "A while ago".
Some jurisdictions, such as Texas and Florida, require the plaintiff to demand a retraction from the would-be defendant. That request for retraction ought to happen prior to filing suit. Otherwise, his lawsuit would be easily dismissed in court. In other jurisdictions (example: Michigan) a request for retraction is a prerequisite only for purposes of punitive and exemplary damages.
Even if Scott's case is presided/obstructed by corrupt judges, of which there are plenty in the US, he will be able to obtain evidence that sets --or helps to set -- the record straight.

A:

What kind of recourse can OP pursue to swiftly clear their name?

The OP's "recourse" is to prove the truth - that he is not a convicted or accused  (by a prosecutor) sex offender - to those who defamed him, who are presumably the bar owner(s), who instructed the bouncer to remove the OP because he was a sex offender; and possibly the bouncer, who may have told Anne that the OP was a sex offender; and possibly others who later on social media said the OP is a sex offender, such as Anne herself.
The facts of who may be a sex offender and who may have falsely asserted someone is must be sorted out, and that's usually done by lawyers before a lawsuit (with a possible settlement from "We're going to sue" threat letter by the OP's lawyer); or in the discovery process of an actual lawsuit; or in court by a jury. 
It's entirely up to the OP to take legal action, hopefully under the advice of a lawyer; and it's not a good idea for the OP to confront the bouncer, Anne or others and possibly complicate his own situation. As for anything happening "swiftly", that's another point entirely.
The OP could sue for damages to his reputation and/or to require the defamers to retract their statements, or for other compensations. Many personal injury lawyers give free initial consultations.
See Defamation | Legal Information Institute for definitions and the laws regarding defamation, libel and slander (which can vary due to jurisdiction; in some areas, defamation is criminal as well as civil). Libel is published defamation, as in defaming someone in messages on social media; slander is spoken defamation, such as what the bar bouncer may have done.

Do they have a strong case for egregious defamation?

The likelihood of "a strong case" is for the OP's legal counsel to determine; they will look at the evidence of defamatory statements, the likelihood of getting monetary damages from the bar and/or the individuals involved, and other factors.

