The answers so far mostly address this point, but the question makes numerous inaccurate assumptions, for example, regarding the circumstances under which a civil action will be dismissed.
There are really myriad differences between civil procedure and criminal procedure that are not easily summed up comprehensively. The other answers touch on some high points, but there are many, many more differences.
The rights of a plaintiff responding to accusations of a crime as a defense in a civil case, and the consequences if the court disagrees, are very different from those in a criminal case. The civil court process and the rights of a party in a civil action still apply. Thus, for example, in a civil case, the facts are determined based upon a preponderance of the evidence, there is not a right to counsel, and the party accused of a crime who refuses to testify under oath can have that refusal to testify held against him by a judge or jury deciding the case.
Misconduct of a plaintiff in a civil case, is simply either just an affirmative defense to the civil relief sought and at most will result in the dismissal of the plaintiffs claim and/or is a basis for relief in the form of money damages or an injunction against the plaintiff on a counterclaim brought by the defendant against the plaintiff, in addition to an affirmative defense by the defendant who accuses the plaintiff of a crime.
Also, not infrequently, allegation of criminal conduct by the plaintiff in a civil case do not suffice to establish either a defense to a civil action or a basis for a counterclaim.
For example, the fact that the victim of a car accident caused by the negligence of the defendant was an undocumented non-citizen, and a violent felon in possession of illegal drugs and a firearm, is not a defense to a lawsuit against the bad driver who caused the accident for money damages from physical injuries and property damages arising out of the car accident, unless it is possible to show that the crimes caused the victim to drive in a manner more negligent than the negligence of the bad driver. Those facts may go to the amount of economic damages that the accident caused (since felons, on average, have poor future employment prospects and you can't recover money damages for future illegal drug dealing profits, for example). But, it is not a defense to liability for the accident. Certainly, in this scenario, the criminal conduct of the victim of the car accident would not provide any basis for the bad driver to bring a counterclaim against the victim of the car accident.
Indeed, in most states, lawyers are expressly prohibited from using the threat of criminal charges to gain an advantage in a civil case, as a matter of professional ethics, and sometimes such threats can constitute criminal extortion (even if the threats are made by a non-lawyer).
On the other hand, in the unusual case in which the complaint filed by the plaintiff, on its face, unwittingly admits to facts that constitute a crime, the civil court could dismiss the case summarily at the request of the defendant if the criminal conduct which is admitted to in the plaintiff's complaint is a valid defense to the civil claim.
Because civil cases have less protection for the rights of the parties than criminal cases, because the parties do not have to face the full economic and legal resources of the state and because the worst case scenario does not involve incarceration, it is frequently possible to obtain relief for alleged criminal conduct in a civil case, even when a criminal conviction was not pursued by prosecutors or the criminal defendant was acquitted. The most famous example of this is the OJ Simpson murder case in which he was acquitted of murder in a criminal trial, but then found liable for wrongful death in a subsequent civil lawsuit and a huge amount of damages were awarded.
