Have a water drinking contest. (Amusement Potential: 5-10 minutes) While the competition is fun, you probably won't feel
too good afterward [AW: Meaning you'll have to pee!]. To give your event an old western theme, slam the cups upside down on the tables after you have emptied them.

Stare at the back of someone's head until they turn around. (Amusement Potential: 2-5 minutes) This works on the "I have the
feeling I'm being watched" principle. Conduct as an experiment, with log book - does this really work?

Have a "Who is less competitive" competition. (AP: 1-3 minutes) Trying to win at this will make you lose. Trying to lose makes
you win which makes you lose. Not trying at all makes you lose which makes you win which makes you lose.

Pick up a dog so it can see things from your point of view. (AP: 3-5 minutes) Think about it: your dog has only seen the house
from a viewpoint from 6" to 2' high (15 to 60 cm for all you metric fans). It's never seen the tops of counters, what you keep
on your desk, the tops of shelves, etc. Try looking at things from its point of view, too.

Pull out a hair, stick in someone's ear. (AP: 1-5 minutes) Best done to sleeping people. Added challenge in having no one else around, because then you can't blame it on anyone else. Try to beat your record number of times before the person catches on.

Dip hand in water, fake a sneeze while flicking water on back of person's neck. (AP: 5-15 minutes) Always a good gag, works great on girlfriend's sister who doesn't know you that well yet who freezes and doesn't know how she should react. To magnify reaction, act like you're not sorry at all for what they think you did. Comment instead on the quality of that sneeze.