Remove all traffic for a specific user agent

Is there a way to exclude, from all properties and all views of Google Analytics, the visitors with a specific user agent?

Note: it's not for spam/bot prevention (I already checked the feature Admin > View settings > Bot filtering > Exclude all hits from known bots and spiders), it's to remove a part of own traffic. I can't use IP filtering because my IP changes all the time, and I use many devices (mobile/desktop/laptop). I also can't use cookies, because often I want to test my website as a random non-logged user. I didn't find anything even after exploring deeply the Analytics UI. Maybe this requires API ?

Solution

(Google Tag Manager seemed a bit labyrinthic for me.)

I finally did this:

Use Custom UserAgent String extension (available for FF and Chrome) and set UserAgent to NoTracking (you can do it specifically for certain websites, i.e. your websites only, see options).

Add this in the PHP page, in the Analytics Javascript part:

<?php  if ($_SERVER ['HTTP_USER_AGENT'] === 'NoTracking') echo 'if (false)'; ?>

It looks like this:

<script>
<?php  if ($_SERVER ['HTTP_USER_AGENT'] === 'MyselfXYZ12') echo 'if (false)'; ?>
(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){(i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m)}) window,document,'script','https://www.google-analytics.com/analytics.js','ga');
ga('create', 'UA-xxxxxxx-x', 'auto');
ga('send', 'pageview');
<script>

This will have the effect of disabling the creation of ga object for your traffic only.

NB: I first thought about disabling GA code for my own traffic via Javascript with if (navigator.userAgent == 'NoTracking') but it seems that the UserAgent change thanks to the extension "Custom UserAgent String" has effect only after the page is rendered, which is too late.