code: def frequent_signups(self):
          
          key = "{}:frequent_signups".format(self.username)
          cached = cache.get(key)
          if cached:
              return cached
          freq_signups = self.eighthsignup_set.exclude(scheduled_activity__activity__administrative=True).exclude(
              scheduled_activity__activity__special=True).exclude(scheduled_activity__activity__restricted=True).exclude(
                  scheduled_activity__activity__deleted=True).values('scheduled_activity__activity').annotate(
                      count=Count('scheduled_activity__activity')).filter(count__gte=settings.SIMILAR_THRESHOLD).order_by('-count')
          cache.set(key, freq_signups, timeout=60 * 60 * 24 * 7)
          return freq_signups
docs: Return a QuerySet of activity id's and counts for the activities that a given user
          has signed up for more than `settings.SIMILAR_THRESHOLD` times