Thanks for your reply. Here's a bit more context. He is an ex-student and the paper is based on an idea we had years ago. It has already been rejected once and the student did little improvements. It is not a bad paper, but definitely not good enough for top-tier conferences. I clearly told him that over a call. His supervisor thinks the paper is good enough but he is not an expert on the topic. In the end I didn't want to insist too much since I am not his supervisor anymore and the paper is not that bad. With my question I tried to be as generic as possible.

@Nemo I didn't know about this journal, thanks!

@sErISaNo It is not ready for a publication, but with some fixes it could go through a lower tier conference. The problem is that the student wants to submit ASAP because they already missed a deadline. I explained them that this will not make any difference, because if it's rejected (which is very likely) they will still have to work on it. I made myself clear, but I am not their supervisor anymore so I won't insist further. The paper is not going to damage my reputation, so I'll let them do whatever they want. I tried to make the question broader by considering also reputation consequences.

@ChristianHennig The paper is not terrible, research-wise it's ok. But it needs more experiments, discussion of related work, and overall make it clearer why this work is important. The student wants to submit to a top venue, that's why I am sure it will be rejected. If it would have been a 2nd tier conference chances would have been higher. The paper can be improved and we'll see if we can make it :)

@FedericoPoloni Author. The student is not within my lab anymore and wants to submit a paper about an idea we had before he left. He wrote the paper alone after he left and was kind enough to add me as author. However, the paper is not ready for a publication. I already have my opinion on the matter, I am more curious about what other people think regardless of my situation :)

Thanks for your reply. I have already asked X once more, and he told me "I am stressed for deadline X, sorry. Will do it asap." In the end, the advisor is kinda right because no one will probably complain that we did not add what we promised (but this may be a topic for another question). As you said, very unpleasant and slightly immortal, but that's how publishing papers works. Yet, I am not happy with X behavior, and would like to convey my feelings in a polite manner: basically that he could have just told me "I don't have time to do it, sorry" rather than keep pushing for 2 months.

@Sursula-they- The question is quite similar (co-author is unresponsive in both cases), but the context is different and I think it matters. The author of the question you linked could simply resubmit the paper ignoring the work to be done by the co-author: it was not asked by reviewers and they never promised anyone to do it. In my case, the work to be done by the co-author is something we promised in the rebuttal. I think it is more pressing. (Thanks btw! Somehow this question did not appear in the related ones when I submitted mine)