I've used this activity many times and have found that my students thoroughly enjoy not telling the truth!
- Give each student a piece of paper (recycled copy paper, preferably) and ask them to write down three things they did on the previous weekend.
- Collect all the papers and redistribute them, so each student has someone else's paper.
- Ask one of the students 'What did you do last weekend?' and indicate that they have to answer using the information on their paper.
- Ask several follow-up questions and tell the student to use his / her imagination to answer. I usually say, in a stage whisper, 'TELL A LIE!' Have all the students stand up, find a partner, and start asking about that person's (imaginary) weekend.