25 C.F.R. § 11.408
Indecent exposure
A person commits a misdemeanor if he or she exposes his or her genitals under circumstances in which he or she knows his or her conduct is likely to cause affront or alarm.
A person commits a misdemeanor if he or she exposes his or her genitals under circumstances in which he or she knows his or her conduct is likely to cause affront or alarm.