Only play this on someone where the atmosphere lends itself. Like with friends at a party. Where everyone knows each other, and can share the joke in good spirit. And of course make sure the person on the receiving end has a sense of humour. And is up for it! Do not pick someone to simply ridicule.

Ok, here goes ...
Have you had too much to drink?
Shall we perform a test to find out?
ok?

You will need:
A soft lead (HB) pencil.
A coin (with milled edges, like a English 10p or American half dollar.
A piece of paper.

Ask the volunteer if they wish to take a sobriety test.
Take the piece of paper and place it onto the table.
The volunteer faces the table, with their back to the other guests.
You face the volunteer, and the other guests, on the other side of the table.

Take the coin and place it approximately in the centre of the piece of paper.
Take the pencil and draw around it, as you say: "I shall draw a focal point on this piece of paper. This is the focal point for the sobriety test. It will test your co-ordination of hand and eye".

Remove the coin from the table.

Ask the volunteer to look closely at the circle on the paper, and try to focus on its location. They are then to close the left eye and stand with their feet together. They are given the coin and are instructed to gently run the coin down their forehead ... and onto their nose ... down their lips ... down their chin ... (all this is one action) and IMMEDIATELY place it as near as they can to the circle on the paper without opening their left eye.

Let them now open their left eye and see their result. Draw around this first attempt with the pencil again. Write a figure 1 in this circle to identify the first attempt. You can encourage their effort if you wish.

Now the volunteer repeats this procedure. This time closing the right eye. Again, draw around this second attempt and write a figure 2 in this circle to identify the second attempt. Are they getting closer? Their feet are close together, right? They are not peeking are they?

This is repeated for the last time. But this time the spectator takes a good look and focuses on the original circle on the paper, and closes both eyes. Then follows the method as before. You draw around this third attempt and write a figure 3 in this circle.

Have they passed the sobriety test?
Geeze ...

have fun, Wulfie

I did that once to my boss just as he headed for a staff meeting. What was cool was everyone thought he was a putz so no one bothered to mention it. He was very angry.