I've just remembered standing in a queue to see The Specials in Coventry before they became well known outside of the city ...
Somebody in the queue had a huge bag of magic mushrooms from which he offered a handful to a couple of students ahead of me in the queue.
The students ate about 20 mushrooms each, waited a couple of minutes, but nowt much was happening so they decided that they hadn't eaten enough. They cadged another 20 each, wolfed them down; still nothing.
They ate 20 more each. By then we were getting close to the door.
Suddenly, one of the students started to get really agitated, followed shortly afterwards by his pal. They fled in terror, and were not seen again that night. It turned out that they were too scared to go home and spent half the night hiding inside a large bush, waiting for the hallucinations to stop!
DON'T TRY THIS AT HOME, FOLKS!