The Michigan statute on indecent exposure is quite old, and quite vague. The Michigan Supreme Court has therefore interpreted the statute in a way that narrows it so that it withstands constitutional scruntiny. The results of that case are summarized in the model jury instructions, which are the instructions the jury would get from the judge if you were to go to trial on an indecent exposure charge. Those jury instructions state:
M Crim JI 20.33 Indecent Exposure
(1) The defendant is charged with the crime of indecent exposure. To prove this charge, the prosecutor must prove each of the following elements beyond a reasonable doubt:
(2) First, that the defendant exposed [his / her] [state part of body].
(3) Second, that the defendant knew that [he / she] was exposing [his / her] [state
part of body].
[Use the following paragraph only if a violation of MCL 750.335a(2)(b) is charged.]
(4) Third, that the defendant was fondling [his / her] [genitals / pubic area / buttocks / breasts*].
(5) [Third / Fourth], that the defendant did this in a place under circumstances in which another person might reasonably have been expected to observe it and which created a substantial risk that someone might be offended or in a place where such exposure is likely to be an offense against your community’s generally accepted standards of decency and morality. In determining this, you must think about the nature of the act and all of the circumstances surrounding the act. [State any other relevant factors, e.g., the age and experience of the persons who observed the act, the purpose of the act, etc.]
So, if you had your genitals exposed in a place where another person might reasonably have been expected to see it you may end up facing prosecution for indecent exposure. Even if you are in your own car, if you are parked someplace where the public might observe what you are doing in your car you may have a problem if your genitals are exposed. The offense is more severe if you were fondling them at the time. Whether the state can prove all the elements of the offense is another matter. This is one of those crimes where all the facts as well as the moral outlook of the jury will make a huge difference. If you are found guilty of indecent exposure, you may have to register as a sex offender and could be sentenced to up to two years in prison, depending on the facts (and if you are a sexually delinquent person it could be up to life in prison). So this is not just a minor offense here. I strongly recommend you do not talk to the police about this unless you have a lawyer present and if you are charged with this offense you will definitely want a good lawyer given the potential serious consequences of a conviction.

