I have a paper accepted at a conference, written together with a colleague (X) and my supervisor. X and I are both postdoc and first authors: writing was done together, but experiments were split between me and X.
The reviews for the paper were very positive, but reviewers still asked for some things: adding some references, giving more details about the experiments, commenting more on some results, and running few extra experiments. In the rebuttal we promised to do most of the things they asked.
The paper was accepted months ago, and I have included the reviewers' requests except additional experiments that have to be done by X.
X has done nothing in months. I have asked them countless times to do the experiments we promised, but they either did not reply or say (in a very polite and apologetic way) "You are right, I am very sorry! I had [sickness / deadline / errand / ...] and could not do it yet. I will do it by the end of the week." This went on for the last 2 months.
Talking to some other colleagues, I have come to know that X is involved in 10+ projects/papers, and is often unresponsive. However, since they are a good researcher nobody has ever complained.
The camera-ready deadline is getting closer and I do not know what to do.
The supervisor (last author) does not care because the paper is already accepted, and does not mind not delivering what promised to the reviewers. ''The paper has been accepted, do not waste any more time on that.''
I would feel really bad about not doing the experiments we promised. How do I confront X?