This joke describes the biggest fear of prisoners in the US. If you drop the soap in the prison shower, you're in the perfect position to be raped! The term is usually used in humor.
"Don't drop the soap". A good example is in Dave Chapelles movie Half Baked
where a character who gets locked up drops the soap. Dont drop the soap!! He gets preyed on my Nasty Nate
The Urban Dictionary Mug
One side has the word, one side has the definition. Microwave and dishwasher safe. Lotsa space for your liquids.
Buy the mug