"Whack" is a slang term used to describe something as being of poor quality or lacking in style. In the context of sneakers, it refers to a shoe that is considered to be unattractive or unfashionable by the person using the term. The term can be used to describe a specific design element of a shoe, such as the colorway or materials used, or it can refer to the shoe as a whole. It is important to note that sneaker preference is subjective, and one person's "whack" shoe may be another person's favorite.