Topics That Don't Work

quantum computing
genetic algorithms
neural networks
EPR paradox
finance & brownian motion
golf ball dimples
fireworks
black holes
dark matter
gravitational lensing
microwave background radiation
parallax
quasars
star classification
supernovae
x-ray binary stars

Topics with known difficulties:

atomic clocks - difficult to describe
three cornerstones of big bang - avoid description of big bang event
tennis racket sweet spots - short on science
quarks - avoid history
maglev trains - avoid unsupported claims of future success
fuel cells - need more science than "descrciption" of operation