Theft & Shrubbery
Source: Bob Mortimer
Gather a group in the suburbs after dark, and seek out a house whose residents are home, but have not closed their curtains. Sneak into their back garden.
Starting at the far end of the garden, chant quietly "We do beg your pardon, we are in your garden". After each chant, creep forward a little and repeat the words "We do beg your pardon, we are in your garden", louder each time.
Keep getting closer to the house and chanting louder until someone in the house notices you. At this point, leg it! You're not allowed to make your escape via the front garden though; you must make your getaway via the neighbours' back gardens, scrambling over fences and hedges as you go.