I would say probably joint worst are:

1. The way you delete things is just incomprehensibly inconsistent.

2. Naming of things is sometimes massively more confusing than it should be. Index? Why not "draft"? Ours/theirs presume some kind of ownership that doesn't exist, and they flip around depending on what command you're doing. To be fair a lot of the naming is decent.

3. The messages the CLI prints are unnecessarily obscure. They presume expertise without being friendly. For example look at the error you get from a submodule update where the commit can't be found. Does it say "Error: submodule points to <commit> but that commit was not found on the remote. Was it pushed?". No it does not. (I can't remember the exact message but I remember thinking how awful it was.)