[tube] shareurl [/tube]
 
where the shareurl is the "share" url YouTube gives you when you click the Share button.
 
Make sure you change https to http.
 

If you use facebook, you can create an album, set it to private (so your friends don't wonder why you keep making weird screen grabs) and take the image URL fro there.
 
Here's how to post from youtube

If  the video link you post goes a bit wonky, and cretes a link nd not a video. Paste the line into Notepad, then copy and post back to the forum, an that will fix it.
 

I've had no problem using Imgur, But then as the Monkey said they all start out fine and over time could hold you ransom. Imgur could be bought out or even just shut down.  If you dig back through my old posts you will soon fine the ones I used Photobucket for, they are all dead links now. 
I use my own web page for important stuff I then have total control. I have a hidden folder so as Kamikaze Say's people won't be weirded out by your screenshots of boring software stuff.. 
 
Thanks for the tip on posting Utube. I'm just in the process of screen capturing some tutorials on CbB so my band partner can learn to use it. I was thinking some others might find them useful.