the salad dressing

"The salad dressing" is an idiomatic expression used to describe a situation where something bad or negative is added to an already terrible thing, making it even worse. This phrase is often used to express a sense of imperfection or loss, at times even degeneracy.

"so that guy did insert thing here"
"yeah?"
"and the salad dressing here is that he did insert other thing here as well"
"woah man"