Could you please add this reason for the close vote?
Custom close reasons are to be used for frequently occurring situations to save the time of the close voters and in particular to provide better guidance to the askers in those cases – e.g, because you do not want to link the respective FAQ post, whenever you close a proofreading request.
If you wish, you can always type up a custom close reason saying whatever you want – but do not expect anybody to agree with you.
background: the quality of this Q&A site is suffering from the increasing number of low level questions. IMHO we need a quality filter.
I do not see any indication for a quality decrease. We have our share of low-quality posts, but we always had.
Can a question automatically be closed when its downvote counter falls below a certain value (e.g. -3)?
Contrary to common belief, low quality is not a reason for closing questions or deleting answers; low quality is a reason for downvoting. Of course, low quality and closeworthiness often coincide, but after all, the reason why we close questions is that there would be a problem with the answers, in most cases that we cannot adequately compare them or there can be arbitrarily many. Or with other words: Questions should be closed, if and only if they cannot be properly answered (except for obvious attempts at trolling, which should usually be flagged as offensive).
In the rare case that a question is low quality but not closeworthy, there usually is no harm in leaving it open as it should still receive useful answers. Moreover, given the rarity of such questions, closing them will hardly increase the overall site quality. Also keep in mind that asking a good question is something that needs to be learnt. The user whose first question has a low quality may ask better questions later on, but often only if we guide them on this matter.
I wanted to close the question “Die weibliche Form des A-Worts” because of its very low level. It even already sounds like sarcasm or trolling.
While you are welcome for flagging or voting to delete obvious attempts at trolling for that very reason, I do not think that this is one – and if it is, it is failed or bad one. Trolling only works if somebody else lets themselves get provoked and this did not happen here.