I've yet to do acid (I'm doing it really soon though, and I'm quite excited), but what you said about the laughs turning your trip really bad is something I experienced on shrooms a while ago.
I was taking shrooms (for the second time, but the first time with others), and none of them had done it before. I kept telling everyone to tell themselves it would be a good trip and it'll be fine... But I was the one who had the bad trip.
They all acted high or drunk or both and laughed at everything, and it gave me a really bad trip. It was horrible. I might end up writing a full report about it, because it was insane.