Hi Rob,How did you find out about the game? Was it related to another game you've been playing more comfortably? Was it a random posting you responded to?
What is your background as a larper and as a gamer in general? (You said you are a new larper. Some more detail would be good.)
How was the neck-sex explained? Did it just start happening? Was it part of the rules? Was it implied on your character sheet but not well documented? Was it mentioned as part of the pre-game speech? If it had been better documented, would that have helped you be more comfortable with the experience?
What was it about the experience that made you uncomfortable? Was it because you weren't sure what to do? You didn't know what the boundaries were? You didn't know this group of people well enough to feel comfortable touching them? You didn't know the game would have so much sexual content when you decided to participate? The person who started initiating it with you seemed like he was out to get his jollies? Was the game mechanic for expressing sexuality too intimate for your taste?
How was the sexual content related to the game? Was a major plot developed around alien seduction or mating rituals or reproductive rights or something? Was a subgroup of players expanding on a part of their characters that was intended to be more subtle? Was the game a thinly veiled excuse for forcing chicks to submit to being groped?.