• submit a diff based on a local commit not in a central repo
• arc patch that diff. Should see this prompt:
  
  This diff is against commit e34e04d093bd6ebdcf415d6812f06e825f28eb76, but the commit is nowhere in the working copy. Try to apply it against the current working copy state? (4d1efa85e9aca5518c22abb07382a6ac00a0e076) [Y/n] n

• say no.

arc will create some arcpatch-DNNN, but it's just an alias for master. Since by answering "no" I asked arc to nothing, so I wouldn't expect it to create any branch at all (or at least, clean up the branch it made but ended up not using).