Recently I've been having a lot of weird looking requests that would end up reported in Errbit. Initially I thought that it is my fault but after double checking all the JS code, I would still get those errors.

Fixing this is quite easy. Undefined/cache/xxx requests come from Complitly malware chrome plugin. Solution to this is quite simple (source). Just add this to every page you have (or every with a form):

<script type="text/javascript">
    window.suggestmeyes_loaded = true;

this will stop the malware script.

The second issue:

ArgumentError: invalid %-encoding (arizona1�0���U��� scottsdale1%0#��U� ��starfield
technologies, inc.1301��U���*��U���+starfield
secure certificate authority - g2/html>)

The rest of weird requests was coming from EasouSpider crawling engine. So just:

User-agent: EasouSpider
Disallow: /

and don't care anymore.