Taking psilocybe mushrooms and MDMA (ecstacy) together. Actually regarded quite highly within the drug subculture. The effects rarely last longer than 8 hours. The effects of the MDMA lend a very upbeat feeling to the user, usually resulting in a positive mushroom trip. Because MDMA is a fairly "reliable" good high, but mushrooms aren't (there can be bad trips), the MDMA high helps to stabablize the mushroom trip.
"What are you doing for the rave on Thursday?"
"I'm going hippy flipping."