I'm going to assume that he has heard the conversation, the shock and outrage expressed by the "lady" and my promises to deal with him. I'm sure that I wouldn't have described to or actually promised the lady quite what his punishment would be and will have left her and Vance imagining the severe consequences of his self-exposure.
What Vance has done is not illegal. Quoting "Nowadays swimming costumes are the norm, but there is no law against skinny dipping. In England and Wales indecent “exposure” is covered by the Sexual Offenders Act 2003 (part 66) which defines an offence if (a) a man intentionally exposes his genitals, and (b) he intends that someone will see them and be caused alarm or distress, punishable by up to two years’ imprisonment. Exposure is only an offence if the man (and the law does not seem to include women) exposes himself in order to cause alarm or distress."
Having chosen a quiet rarely frequented spot, it's clear that he didn't intend to be seen in this state nor did he do it to cause alarm or distress, even if the lady claims that this was what he did cause.
I'm going to get him to tell me exactly what punishment he thinks he should suffer, bearing in mind the lady's perceived outrage and my response - and then give him precisely nothing apart from an arm round the shoulder and advise him to be more careful in future! The lady. meanwhile, can have her own (wet?) dreams imagining the punishment I will have exacted from Vance.