This is a well known game in Spain, but I had never thought of using it in class until my teenage students asked if they could play it. It is a typical group guessing game where some of the players know the rules but others are unaware and have to guess what is going on.
You will need to have the class sitting in a circle (or semi circle if you lack space). Some of the students must go out of the room while you explain how to play the game. These students are the "psychiatrists". These students must never have played the game before (it is better if they are stronger students). The others are patients. Tell the patients that they have an illness. This is usually that they think they are the person sitting to their right (but if you want to play the game on other occasions, change this every time e.g, the person sitting opposite, to the left, two to the right etc).
Then, invite the psychiatrists back into the room and tell them that they must diagnose their patients by asking questions. The patients must answer as if they were the person to their right, e.g to the question: Are you wearing jeans? If the person to your right is wearing jeans, say yes. Students must be careful not to look at this person as this will give the game away. If the patient does not know the answer to a question, they must shout "psychiatrist!" and everbody changes places. If a question is too revealing, any player can shout "psychiatrist" at which point everbody, again, changes seats.
The game continues until the psychiatrists correctly diagnose the illness.
This game can be played at any level; at higher levels make sure the students ask more complex questions using different tenses, the passive etc.