Watch 18+ Videos On Youtube Without Signing In

. First get the Url of video you want to watch. As shown below.
http://www.youtube.com/watch?v=4Xkh6j7RMqk
2. Then copy the Video Id. For above link video Id is 4Xkh6j7RMqk
3. Now paste the Video Id in the link given below.
http://www.youtube.com/v/VideoId?fs=1
Replace VideoId with the Id you copied in Step 2
4. Now the url will become as shown below.
http://www.youtube.com/v/4Xkh6j7RMqk?fs=1
5. Done.