Originally from http://dbhs.wvusd.k12.ca.us/webdocs/Humor/Funny-Metric-Chart.html (page no longer there).
1012 microphones = 1 megaphone
106 bicycles = 2 megacycles
500 millinaries = 1 seminary
2000 mockingbirds = 2 kilomockingbirds
10 cards = 1 decacards
1/2 lavatory = 1 demijohn
10¯6 fish = 1 microfiche
454 graham crackers = 1 pound cake
1012 pins = 1 terrapin
1021 picolos = 109 los = 1 gigolo
10 rations = 1 decoration
100 rations = 1 C-ration
10 millipedes = 1 centipede
3 1/3 tridents = 1 decadent
10 monologs = 5 dialogues
5 dialogues = 1 decalogue
2 monograms = 1 diagram
8 nickels = 2 paradigms
2 snake eyes = 1 paradise
2 wharves = 1 paradox
10¯6 phones = 1 microphone
106 phones = 1 megaphone
10¯2 mental = 1 centimental
10¯1 mate = 1 decimate
1012 bulls = 1 terabull
10¯12 boos = 1 picoboo
10¯15 bismol = 1 femtobismol