h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Equipment: two office chairs, two garden hoes, two binders, people, and an endless number of halls to play in.
Players: Two for each team, one to sit in the chair and, well, joust, and one to push the chair around if the other guy decides to run, or hold it still if players are stationary (otherwise you end up going backwards), plus a referee.
History: Well, my friend was in Office Depot (an office supply store)and he discovered, whilst riding around in a very expensive, brand new office chair that the ladders used to reach merchandise high up have, for some unknown purpose ordinary garden hoes hanging off of them. He then grabbed said hoe as he was whooshing past one and discovered it was weighted just right to stab at things. He thought, it would be fun to get a bunch of guys together and practice this. After a round or two, and many painful bruises, he discovered a shield was needed. Hence the binder.
Rules: Um... games are, well, as long as you can manage to play before you get kicked out of the store (pretty long if you're smart and stick to the back half) and the winner is the guy who takes the most hits with the least bruises. In some cases, there are boundarys, ranging from one aisle to an entire store. Due to stealing laws here in Canada, they usually don't get anywhere near the doors of the store, so it's not an issue. Penalties ensue for one guy just turning tail and running away, it's cowardly, and for some reason, cowering in a corner attracts more attention than fighting with hoes does. The ref is mostly there to call the start and inform individuals when the group as a whole has been kicked out.
That's about all, go forth into the world and annoy as many managers as you can.

Oh yeah, and you can usually only get away with one game per store, so be careful. Of course in larger cities this isn't a problem, but in one store towns it might cause one when you can no longer buy pencils due to being kicked out of the only stationary store in town.

you can also try Meyering. Any number of people can play. It consists of entering any local 24 hour super store (wal-mart, asda, meyers, giant eagle)...hopefully in the dead of night in "supicious" looking clothes. (long trench coats work wonders!) then proceed to walk eratically around the store picking things up and putting them down again somewhere else or passing it on to a fellow person for them to put somewhere else.. The object is to see how many undercover police men you can get to follow you around the store. wrecking havic in the toy isle can be an added bonus.