Though not strictly a joke, these are funny anyway!

Some dubious metrics:
10**21 piccolos = 1 gigolo
10**15 coats = 1 petacoat
10**12 bulls = 1 terabull
10**12 microphones = 1 megaphone
10**12 pins = 1 terrapin
billions and billions = 1 Sagan
10**9 lows = 1 gigalow
10**9 antics = 1 gigantic
10**9 questions = 1 gigawhat
10**6 bicycles = 2 megacycles
2*10**3 mockingbirds = 2 kilo mockingbird