How to behave at orgies/swingers parties

We have been around a bit and always find it amusing when we go to parties and see how different groups behave. We like and prefer the parties where the lighting is soft and sexy, but you can still clearly make out who is touching you and wanting to play (in this day and age consent and respect is a must when it comes to playing). However, we have recently experienced people barging into rooms where multiple couples are playing and having them turn off all the lights with out asking. We enjoy getting to know people a little before we play over a couple of drinks in some sexy underwear. We find it helps relax and set the mood for the evening. We find that a simple "no" or "not just now, thank you" usually works when you do not want to play, but at times have found people becoming increasingly forceful or agressive when polite declined. We are hoping that other experienced 'swingers'/party goers will add to this thread and help enlighten any newbies about how to correctly behave at parties. Every party is different and every party can be great, but if you get one person not following the basics it can turn a great night of fun into an earth shattering evening of regret. So come regular players, groups, and horn bags lets revise the rules and share some stories of good times and bad.