Dear Etiquette Expert,
What is the polite way to tell a friend, "no thanks, but I don't think I'd like to attend an -ahem!- "adult" party for XYZ Pyramid Scheme, where a pushy saleswoman will attempt to pressure me into buying crap I don't need (or at the very least, giving her my contact information so that she can spam me for the rest of my life)"?
How about, "Friends don't let friends pressure them with direct sales" or "I will only voluntarily subject myself to guilt trips given by elderly family members (and sometimes Al Gore), not those given by a type A suburban soccer mom and a room full of my so-called friends"?
Another tactic would be to start an urban legend. For example, you could try the old "A friend of a friend told me that direct home sales parties are just fronts for helping drug dealers and thieves launder money. I heard that at one party, a gang of bandits bust in and stole everyone's identities. With guns."
Or you could just say no, firmly but politely.
It's up to you.