These ads make me sick, also. I have a new computer and only I use it, so there IS NO HISTORY of visiting these kinds of sites on my computer, yet I still get the ads.  And, I totally disagree with the other commenter, who seemed to imply these ads are appropriate for 13+ year olds.  They certainly are not.  They are sexually suggestive, with pictures of scantily clad women taking off their pants and in bras, with comments like "tired of an empty bed?" and "no strings attached".  
I have son and can no longer go to youtube with him without being bombarded by the ads.
I researched how to flag an ad as inappropriate, but can't figure it out. Youtube also doesn't have contact information for me to let them know.
I will try to erase the cookies, but I doubt it will help.
Suggestions anyone? How can this be stopped?? Does anyone know how to flag an ad???