Adblock time to time can’t handle this simple task to hide pre rolls on YouTube, so, you can use this simple trick.
Just update your hosts file using these lines:

127.0.0.1 ads.youtube.com
127.0.0.1 s0.2mdn.net
127.0.0.1 s1.2mdn.net
127.0.0.1 googleads.g.doubleclick.net
127.0.0.1 pubads.g.doubleclick.net
127.0.0.1 ad.doubleclick.net
127.0.0.1 static.doubleclick.net

Done!

Next level of craziness — host file with 15K+ lines, check this out.