You can also try (from git remote):
git remote --prune guy
With:
prune
Deletes all stale remote-tracking branches under <name>.
  These stale branches have already been removed from the remote repository referenced by <name>, but are still locally available in "remotes/".
With --dry-run option, report what branches will be pruned, but do not actually prune them.
See also "Difference between git remote prune and git branch -d -r"
if guy is no longer a valide remote repo, then:
git gc --prune=now
will clean up those branches (along with some unreferenced commits, so use it with caution)
See more at "How do you Remove an Invalid Remote Branch Reference from Git?": it is usually more safe to just go with: git branch -rd guy/badbranch if possible, but if this doesn't work, then git gc --prune=now can also be a solution.