Shortest unused Twitter #hashtag

What is the shortest Twitter #hashtag that has never been used? As an additional constraint, let’s focus on the lexicographically first hashtag composed of ASCII letters only of that kind. Let’s skip dessert and use Python and the Twitter Search API to find out:

import urllib
import json
import itertools
import string
import time

k, max_k = 1, 10
while k < max_k:
    for tag in itertools.product(string.ascii_lowercase, repeat=k):
        tag = ''.join(tag)
        print "Searching for #%s" % tag
        search_url = 'https://search.twitter.com/search.json?q=%%23%s' % tag
        while True:
            search_result = json.loads(urllib.urlopen(search_url).read())
            if 'results' in search_result:
                break
            print "Wait a few seconds because of Twitter Search API limit"
            time.sleep(5)
        search_result = search_result['results']
        if not search_result:
            print "Unused hashtag: #%s" % tag
            k = max_k
            break
    k += 1

After a few minutes, the result: #agy. What could we use that one for?