Long long ago I filed a bug against TogetherJ, where I determined empirically that they had a bug with monorepo/separate compilation units that resulted in n^5 time complexity for loading multiple project files at once. For the last data point I started loading it at 5pm one day and then it finished at 11 am the following morning. They gave us a workaround that got it down to around 20 minutes, the patch made it a little bit better than that but that was still a long time.

I'm sure I've found factorial complexity code, at least in the design phase, but that's the worst one I've encountered in the wild.