Long ago I noticed one video on Youtube, which I could see when it was embedded, but not on its normal video page. There you could see the message:

Title of the Video
This video blablabla Content, for you blablabla

To see the video you would need to login into an account where you set your age to 18+.

After some tests one can say that most videos can be viewed with this trick :)

nidx/yt18/ (does not work anymore, but still works with mpv)

Just rewrite it from

http://www.youtube.com/watch?v=ID or http://www.youtube.com/verify_age?next_url=/watch%3Fv%3DID

to

http://www.youtube.com/embed/ID

Search for „embed youtube video“ in your $SEARCHENGINE …

I know, you can create an account and set a wrong age, but the url rewriting is very helpful in conjunction with a slow proxy.<br />Also I wonder in many cases, why Google „censors“ such videos…