I had a similar experience once. I was filming (by filming I mean pointing a handicam) a scene for a web series I used to make with my friends. The premise was essentially Reno 911 mixed with the ghostbusters.
This particular scene involved a sting on an alien prostitute. There was a simulated blowjob between my friend (in a terrible alien costume) and an "officer." Thing was, we were filming this at 3 AM and the only place well-lit enough was the back park area of a local church. Once we've gotten our shots, as we are walking back to the car, four police cruisers zoom around the corner, and four officers with guns drawn run from either side of the building. My five friends and I are all ordered on the ground, face in the concrete, hands behind heads. (By the way, this is in McDonough, GEORGIA) Half an hour later they let us go, our pants all thoroughly shat.
EDIT: If you care to know,
this is the episode that ended up coming from that event. I'm fairly mortified to share it.