Stand up and act indignant. Demand that the boss tell you the 'real' reason this meeting has been called.
Spill coffee on the conference table. Produce a little paper boat and sail it down the table.
During a meeting, each time the boss makes an important point, (or at least one he/she seems to consider important), make a little noise like you are building up to an orgasm.
Stay behind as everyone else, including the boss, leaves. Thank them for coming.
Give a broad wink to someone else at the table. In time, wink at everyone. Sometimes shake your head just a little, as if to indicate that the speaker is slightly crazy and everybody knows it.
Arrange to have a poorly-dressed young woman with an infant quietly enter the meeting, stare directly at the (male) speaker for a while, burst into tears, then leave the room.
Bring a hand puppet, preferably an animal. Ask it to clarify difficult points.
When there is a call for questions, lean back in your chair, prop your feet up on the table, smile contentedly, and say, "Well, here's the way I see it, J.B..." (or any other impressive-sounding initials that are not actually your boss's.)
Complain loudly that your neighbour won't stop touching you. Demand that the boss make him/her stop doing it.
Bring a small mountain of computer printouts to the meeting. If possible, include some old-fashioned fanfold paper for dramatic effect. Every time the speaker makes a point, pretend to check it in one of the printouts. Pretend to find substantiating evidence there. Nod vigorously, and say "uh-huh, uh-huh!"