Let's assume for the sake of argument that you have an issue with the following:
this was the least offensive way someone ever 'shopped' for me
(implies that all ways are offensive)
Previous edit (removed but still caused some comments):
She's working, and since she's working as a cashier and not a prostitute, her job description doesn't involve being picked up by random guys. The only thing that those jobs have in common is that they require the worker to be nice to their customer (most of the times). This is, of course, an exaggeration, but I hope you do get the point
(comparing flirting to prostitution/sexual abuse is extremely offensive and damaging to youth)
Overreaction that you "must not complain about":
your number might end up in the bin with a dramatic gesture [...] you might be labeled a creep and denied access to the store, depending on how much this tends to upset her. If you get declined, however rudely, don't go complaining.
(justifying unrestrained unwarranted aggression over a ... "want to know you here is my number"-note; not all courtrooms would take lightly a "you are a creep!" in the above scenario; a simple firm "no" is a better option)
So, how do you explain all that without commenting?
On other SE sites:
You'd leave a comment, and down vote such answers.
You could also leave a better answer on the question, showing the correct answer. Make sure you include a good explanation as to why the other option should not be used.
On this site however ...
When we say that comments need to "ask for clarification" - we mean that.
Your comment is an argument. It's stating your preferred action and why the answer is wrong. This is not asking for clarification. This is non-productive.
... you can't.
This goes against what happens on (perhaps all) other SE sites. Even on sites like Worldbuilding where answers can be based on fantasy, people are allowed to disagree constructively in comments.
Downvoting: Lots of users suggest posting your own answer or downvoting (DV). This has minimal (often negligible) effect on the parts of the answer that were wrong. Firstly, many (if not most) votes on Hot questions come from non-regular visitors that most likely have no DV rights. So DV is impossible.
Answering: when a problematic answer has 100 score would mean your answer is in the bottom, and the odds of being read are smaller than the answers at the top. Youtube has similar issues with its comments. If they simply let highest voted comments remain at the top, then you'd rarely see new comments. This is fixed by their sorting algorithms, which however don't exist on SE sites. (no, the option to sort from newest to oldest isn't how YT works..)
Criticism or removal of wrong/harmful points can't happen by posting my own answer. Some users will never even know that those points were wrong without highly upvoted comments that state them.
Yes, all the above could theoretically have an effect, but in our real world scenario they will most likely have no effect. Insisting that the above are a solution to the problem is wishful thinking.
Therefore, there is currently no easy way to tell an answerer that you think their answer needs work. Your comments will most likely be deleted.
To clarify my answer based on comments here (and some offensive comments I've seen in IPS chat):
I am NOT saying that the poster has issues. I don't hate him either.
I don't disagree with the solutions the poster suggests. On the contrary I agree with most of them.
I don't want the answer deleted, or forcefully edited.
Rejecting someone that's flirting is perfectly fine (duh); calling security over someone insulting, making a scene, acting in a strange way, etc, is perfectly fine. (there are infinite strawman arguments of this type, can't address them all, sorry)
Also, if you disagree with my answer, feel free to comment and point out what you disagree with. If I am wrong on something, I'd love to hear it. Criticizing wrong ideas is why we don't still worship rocks. So please correct me.