in git, what ways are there to "lose" a commit in a way that you CAN'T recover using the reflog (so that you need to iterate over every single commit in the repository if you want to find it?

The only ways I know (using git's normal tools) are:

* using `git stash drop` or `git stash pop` to drop a stashed commit
* waiting 90+ days to try to recover the commit (so that it expires from the reflog)
* explicitly deleting the reflog in some way (rm -rf .git, git reflog expire, etc)

@b0rk if it's a commit you haven't fetched yet from a remote repo, and the ref is deleted, the remote repo usually won't give it to you just from the SHA, even if it is still available at another ref.
@mjd
The most alarming word in that post is "usually".
@b0rk