Please tag as "humorous".

How can a comment (it's not in the article itself) constitute copyright infringement? Man, you're crazy on 'copyright'. What a bummer. Disrespectful to freedom, if you ask me...

I know Tatoeba should respect copyright, but I think this sort of usage (quoting one sentence from a larger work) should fall under the academic fair-use exemption. Reviewers are always allowed to quote brief passages from a published work,.

Also, I saw today that a full-text database gets around the problem of people attempting to extract one of the database's component works, which may be under copyright protraction, by the simple expedient of archiving 195 words, then deleting the next five, and so on. Because every extract of 200 words or more will therefore be missing at least five words, it will not be possible for an unscrupulous person to reconstitute the complete text, but users of the database will still get useful statistics on frequencies of individual words and collocations.

It seems to me that no harm comes to the original writer if this quote (admittedly the most memorable and epigrammatic portion) is posted. We could always have a tag that says something like "author unidentified." This could be explained in a legend or linked text as "Tatoeba will gladly give credit to the original author of any text which we have failed to properly attribute."

Quit marking sentences as undesirable if there is no consent reached.
There is no harm to the original writer whatsoever if a small excerpt gets posted, and therefore no incentive to enforce copyright.