A person who helps(ed) you on an acid trip. This person would usually have prior experience using LSD, and would be there to guide the individual through their journey to the center of their mind by way of the introduction of music and transcendental meditation. It is not necessary for the Acid Coach to be taking acid at the same time as the trainee.
Alec's Acid Coach totally screwed up. When Al started coming on to the acid, he was left to go through it alone his first time. He started watching some violent TV show and had a real bad trip. That dude was a total downer.
When I took acid for the first time, Kevin took me on a long drive in the mountains, listening to some Ravi Shankar. I totally connected with the Universe, man! Kevin makes a great Acid Coach!