* Unfashionable: This is the most straightforward and common option, directly negating the word.
* Anti-fashionable: This emphasizes a deliberate opposition to fashion trends.
* Infashionable: This is less common but conveys the same meaning as "unfashionable".
* Afashionable: This is less used, but could work in some contexts to suggest a lack of fashion sense.
The best choice depends on the specific context and the nuance you want to convey.