The usual amount of bad information here, I see.
It's very doubtful....VERY doubtful...in my mind that the police would respond to a complaint of this nature in the first place. So many "sick" Californians have medical marijuana recommendations today that it's just not worth the time to go looking into what amounts to a personal possession complaint - for which you're not going to be arrested for in California anyway.
However, IF the police were to respond to a complaint (and I really have a hard time imaging that they would), the only person liable for anything is the person in possession of the drug or the person who admits to it.
Bottom line: you are at very little risk in the situation you've described. If it concerns you, then you should consider asking them to respect you by not doing it anywhere around you or just don't go to the house to begin with.
I AGREE WITH MIKEYSCO-----------VENTURA COPS ARE SHADY THO-------------THEY PLANTED A JOINT ON A FAMILY MEMBER OF MINE AT A CONCERT THERE IN VENTURA------BACK WHEN WEED WAS A BIG DEAL.....AND HE BEAT IT AFTER A WHILE AND A TRIAL....
Well, if justice prevails, you get the sad experience of watching your friends get led off in handcuffs. You'll have to finish the steaks and hamburgers yourselves. Your call on whether you drink up all the beer or not.
The hazard, of course, is if the police get the "arrest them all and let God sort it out" mentality. You'll be hauled off to jail, where you can bond out. Again, any charges you face should be dropped, and if not any competent lawyer should get you acquitted. That's not cheap, though.
One thing you have to be scrupulous about is to not handle any drugs. Don't even pass the bong from one smoker to another smoker. So long as you don't do that, technically, you are completely innocent.
No problem for you. Only the guy in possession of the marijuana + the paraphernalia.
If it was me, I wouldn't even go - if theres going to be weed. You are drug free people and you shoudlnt have to be around a bunch of trashy drug addicts.