I often wonder what my name brings to mind in other people - it often results in a chat ban ban for me at online live casino tables.
It is a term used in casinos for when a stack of 20 chips has a chip in it that shouldn’t be there.
For example:
Customer buys in for £500.
Dealer thinks they are passing to the customer a stack(20) of £25 chips.
Eagle eyed inspector notices one of the £25 chips is actually a £5chip and shouts out ‘dirtystack!’
Dealer goes ‘uuugh?’
looks at the stack of chips, takes out the £5 chip, replaces it with a £25 and passes out the correct amount to the customer.