Bitrex (Denatonium Benzoate solution 5% w/v) sorts out problems enforcing handwashing.
The bitterness at that conc lasts for hours.
(
FeralCatMan Unusual disease collector.,
Thu 25 Oct 2012, 21:18,
archived)
I like to leave them with just enough doubt.
(
An Egg ,D,
Thu 25 Oct 2012, 23:13,
archived)