Great thread. I can't really compete with the OP, but back in 197something, I used to hang out with a group of people who'd get together for a friday evening jam in someones house. Many substances were consumed and others changed hands. One friday while we were playing amidst the mass of stoned and tripped out bodies, there was suddenly a frantic banging on the door. Several of us went to investigate, and found our regular drummer (no surprise there then!) with wild eyes gibbering about being followed by the police. As one or two people left rapidly by the back door, we tried to reason with him (and suggest that leading them to us might not have been the smartest move).
I was trying to think what to do but kept asking the people in the house to turn the bloody music off as it was getting a bit weird and hypnotic and starting to freak me out. They looked a bit worried when I said that, and finally someone told me to look at my hands (shades of a Castenda dream) and I found that the only music playing was my bass.
Never really lived that one down!