A laundry detergent brand is currently running an ad campaign with the tagline “Style is an option. Clean is not.” Obviously, what they mean is that cleanliness is required while stylishness is not; but the way I interpret the tagline, what they’re actually saying is that stylishness is available as a possible choice, but cleanliness is impossible — it’s not on the menu.
Before I drive my family nuts by muttering “optional, optional, optional ” every time the commercial comes on, can y’all confirm that my distinction between option and optional is grounded in reality?
option (n): an available item that can be chosen (or not).
optional (adj): not required; elective.
 Yeah, yeah, I know, too late… :p
I would agree with your interpretation of the difference between the two. From Wiktionary:
Based on the definition of option, the advertisement tagline reads:
Style is [one of the choices which can be made]. Clean is not [one of the choices which can be made].
This implies that there are some choices available to the customer, and that one of the available choices is “style”. It also states that “clean” is not one of the available choices. To be fair to the advertisers, this does not mean that clean is not part of the product. It could be included by default and therefore not an option. At any rate, this does not quite convey the intended meaning of the tagline.
Using optional would be a much better choice: “Style is optional. Clean is not.” Based on the above definition, this sentence would read:
Style is [not compulsory]. Clean [is compulsory].
If that advertiser really wants to use the phrase an option, a similar meaning could be found in the sentence: “Style is an option. Dirty is not.”
Note: it appears that you are not alone in questioning this tagline: