They are not my pants

I've heard people have said it but did not believe it.

When I was a police dispatcher several years ago, I was riding with my friend Paul and we stopped this guy staggering down the street.  We both saw him drop something out of his pocket and Paul found a bag of some drug.  Paul asked the guy if it was his and he said no.  Paul told him that it came out of his pocket.  And the guy actually said it:     They are not my pants.