Sometimes you need to work on your acting skills. Sometimes you just need to have fun. This exercise is the best of both worlds.
Two people perform a grounded scene. Don’t try to be funny, just keep it real and commit to what’s unfolding between you and your scene partner. A third person provides fart SFX from the side.
Try it at your next rehearsal.
Photo © Jim Goad for BCIF
People and Chairs 
For even more of a challenge, do it in front of a paying audience… 🙂