While there is clearly much variation in what you will get if you ask for a "mind eraser" at a bar, there is One True Way to make a mind eraser such that it will deserve its name.

You will need:

Choose a container of at least 8 oz. Taller, skinnier glasses are more fun. Assuming it's been kept cold, pour a shot of Jägermeister into the bottom of each glass. (Nobody makes just one mind eraser, as no one should be doing them alone.) Stick a few straws into each glass, and then fill each glass with ice. Dump in a shot of vodka, and top off (i.e. fill the glass) with a light soda of your choice.
If there are two drinkers, they should face eachother. More will probably need to arrange themselves in a line. Leave the glasses on the table, bend over, exhale, take the straws into your mouth, and on someone's mark, suck and swallow like you have never sucked before. Done right, you will taste nothing. Cry uncle and you might puke all over the table if you don't like licorice.

A note on the Jägermeister: Some people like to put the ice in first so the Jäger is chilled more by the ice. This tends to spread the taste of the spirit around more, which to other people is contrary to the idea behind the drink. However, if you haven't been chilling your Jägermeister, it is a good idea to add it after the ice. Try it both ways and stick with what you prefer.

A note on the vodka: it can be as shitty as you like. No need to waste your Absolut, Gray Goose, or Ketel One on this drink. Popov or anything else in a plastic jug will work just fine.

A note on the soda: while tradition clearly dictates the use of plain soda water, any light crisp soda will work fine. Red Bull is not a bad choice if you have trouble staying awake while drunk; just have a glass of water handy to wash it down.

The mind eraser, along with the irish car bomb, has become a favorite of noder gatherings.