Here's one story from a club that happened to me...
I was rolling hard and just came out of the bathrooms after doing a bump of k. I walked up to the sink to wash my hands and there was a girl sitting on the sink basin wiping sweat off her forehead and she started chatting with me. After a few, she asked what I took...this was back in nyc club days when cops were just starting to crack down on things...I said, "Nothing."
We chatted a little more. She was kinda coming on to me, which is why I continued chatting. Then, she said again, "You're really not on anything?" Now the k was hittin me and I was rollin hard and feelin really good, so I was just casually like,"Oh, I'm on all kinds of shit." She got a real serious look on her face and said, "Really?"
I looked up in the mirror and saw a bunch of bouncers who must've been watching start to head towards me as the girl made a signal with her eyes to them. My heart jumped out of my chest and I turned and beelined it through the crowd. The club was huge, so I was able to disappear in the crowd...they never found me.
This was over 10 years ago, but my rule even to this day is not to even talk to anyone at raves or in clubs about drugs if I don't know them. Not knowing them means I didn't know them before I went in. You need to be very careful of undercovers trying to strike up conversations very casually...they know people are open and vulnerable while rolling.
That's why I say be careful of everyone you didn't know before you went in because one of your friends that's fucked up might have just met someone they think is cool and introduce you to them and you assume they're cool cause your friend made the intro.
Don't buy inside raves and clubs and don't tell anyone you're high. Too dangerous.