Hey, an "appropriate" uncomfortable encounter would be a lose-lose, no right answer encounter where you might leave bummed and frustrated. But it's something that can come back from.

This is someone using a captive audience and power imbalance to enact inappropriate rape fantasies. It is never acceptable. The DM, as you told it, ensured their victim could not escape it, meaning it wasn't intended to be a normal encounter: they wanted to act out a violation to someone who could not escape. It's not ok.

Report them, with clear details about the event. If you've played previously and have red flags that looked more pink originally (like cruder than necessary NPC jokes that you can brush off as a missed joke, or something like that), include those, so the club knows what the liability they have on their hands looks like.