Call something unsavory if it's unappetizing, tasteless, or morally offensive. Curdled sour milk is pretty unsavory, as are the dirty details of the latest political scandal.
The adjective unsavory was formed by merging un, meaning “not,” with savory, meaning “pleasant, agreeable.” So if it's unsavory, it's unpleasant. First used to describe revolting tastes, unsavory now also applies to just about anything that figuratively leaves a bad taste in your mouth. Mobsters do all kinds of unsavory things to the people that cross them. So you probably shouldn't hang out with such unsavory characters.