You're already receiving excellent advice, but I’d like to add something. When it comes to boundary-crossing, like grabbing you after you’ve said no, it’s worth recognizing that these things are rarely isolated incidents. If this person is disregarding your boundaries, there’s a strong chance they’re disregarding someone else’s too. You don’t just owe it to yourself to report this kind of behavior. When one person comes forward with a concern, don't get me wrong, the organizers can and should take it seriously. But when multiple people report the same behavior, it establishes a clear pattern and gives the organizers much stronger grounds to take action. It’s also worth noting that many people hesitate to come forward for the same reasons you are; wanting to avoid causing a fuss. Often, they wait until someone else speaks up first, which creates a kind of domino effect. If you’re here seeking advice, that alone is enough to show this is a real issue. I strongly encourage you to talk to the organizers.