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460: Put asbestos in the thermo device and watch as the proctor flees.

Pull your phone out during a test and start looking answers up

462: Make your ringtone Rick Astley, and make sure the volume is all the way up, and have someone call you during a quiet test session.

463: Bring a box filled to the brim with batteries and bugs, and tell the proctor when he/she gets mad that you couldn't read the Battery Buggy rules because the font was too small.

464: Steal all the spaghetti from Mystery Architecture, cook it, and sell it to other teams for a profit

I've actually done the following:

465: When the Dynamic Planet test asks you to name the continents, write a half-page essay on how "we are one Earth" and should not divide ourselves (We got 2nd somehow)

466: Mission Possible (Div B so no fire) was held in a library and while waiting for the judges to come over, we read random books around us

467: Sitting on a wall and promptly falling off, causing someone from another team to choke on ice-cream out of shock

468: Starting the 'We Will Rock You' chant during the awards ceremony and get the whole crowd to do it, annoying the event supervisors
Bonus points for doing this during Dynamic Planet or Rocks and Minerals

469: Attempting to start friendly conversation with other teams during the last 15 minutes of Crime Busters

470: Creating a DIY Stress Ball with Gelatin and Water in Crime Busters

471: Telling the Dynamic Planet proctors geology puns

This I've seen another team do:

472: Having your Battery Buggy crash into a wall, rebound back, crash into the wall, rebound again, and repeat this several times

This has actually happened to me before, and I'm still salty about it:
473. Bring a cheat sheet for another event into fast facts...

474: Literally throw the cheap 3 ring binder at the test, and then watch as the ~500 pages fall out and bury the adjacent team's test. (Bonus points if it's your rival team)

Have walkie-talkies in WIDI

476. Call someone on the phone during a test. When the ES asks what you're doing, say you're using your "Phone a friend".

477. Edit the wiki during a test.

478. Burn the plastics in forensics until the proctor can smell them