My worst collab/group project experience definitely has to be my final semester project during my undergrad.

We were a team of 4 including myself and would meet every day to work and every day:

1. My teammates would show up late
2. One of my teammates’ girlfriend lived in my apartment and shed just show up every day and waste our time and make him never contribute (He LITERALLY never did any work and got by with no effort)
3. The other 2 on the team didn’t know anything and never made efforts to learn

I literally did the entire project on my own (Code the full project, make presentations for all the reviews, and teach the other 3 every step of the way).

TLDR: I topped my batch and got 199/200 whereas everyone else were 190 or below, and I went on to publish that project in a Science Journal (Again, with no efforts from the team)

Sounds like a typical undergrad project! I think the worst one I did, I helped one of my teammates learn how to install Linux and use git, and then I never saw him again even at the final exam. He literally contributed less than nothing to the project because I could have used that time to do something else. My other 2 teammates were international students who had a very different view on how college was supposed to work, so didn't contribute anything to the project either. Based on what they said to me, I think they were intending to boost their grade by openly cheating during the final exam. Of course, not only did my school not allow that but they took a lot of active measures to prevent it. One of them had a really shocked look on his face when we filed into the gym with desks clearly set up to prevent cheating, and sat down to receive not just our final exam papers, but the group evaluation papers, where we could evaluate how much each group member contributed to the project.