i think you should shower less, or think less, or some combination of these two

Metaphors were never meant to be a perfect analog in every aspect.

Verbal analogies aren't mathematical formulas.

What about unpopular opinions? I thought all buttholes were unpopular. A term like that implies that there are also popular opinions, and therefore also popular assholes. What kind of asshole would be popular?

I actually know two people without assholes… although they both have a tremendous amount of opinions all the same.

Can you describe the smell of your asshole (please)?

I shall not today attempt further to define the kinds of odors I understand to be embraced within that shorthand opinion, and perhaps I could never succeed in intelligibly doing so. But I know it when I smell it.

Except it's "opinions are like assholes, everybody has one", they aren't saying your asshole is an opinion.

Follow-up question: what’s the goatse of rhetoric

No? If opinions are similar to assholes because everyone has one (with the exception of a few people who are literally born without assholes) then asking someone to 'explain' their opinion would be akin to asking them to either describe their asshole (possibly including, but not necessarily, its smell) or to describe the origin of their asshole depending on which version of 'explain' you are using.

Ah, so when dogs sniff each others' butts, thats like a canine mind meld

It's like asking them to fart in your face.