What have you been watching then!?!?

Try Settings>Applications>Manage Applications, press Menu again then Filter>All. Scroll to bottom and find Youbtube and try clearing data and cache.

This should work.

 

Or you could go onto the youtube app, then click the bottem left button on the phone (the one with 4 squares over it). Then settings and its the 3rd down.
Im wondering the same as rosered, what have you been watching?

 

D'oh... didn't even think of looking in the app!

Don't really use it so had to view a video and then see if I could clear the cache.

 

There are so many apps out there which can clear youtube, maps,gmail, browser, market etc search history.. I use History Eraser

https://market.android.com/details?id=mobi.infolife.eraser