The other definition here claiming that yin yang refers
to anus is correct, and older people
in certain regions of the US know this
very well. This
site is for "slang" usages, not the formal dictionary definition which would refer
to the Chinese symbol
. When a person says
something like, "Wow, this
store has widgets
up the yin yang", it does
not mean plethora. Rather, it's a substitution for the word ass. And in a sexual context, yin yang does
to the anus. "Taking it up the yin yang" is probably the most used phrase, although it's now somewhat antiquated, and it means taking it up the anus, or male/female part which is common to men and women, which is how the word was derived
since the Chinese symbol
represents the male/female balance.
The drug smuggler stuffed it up his yin yang.