It would be inappropriate to me if I saw that ad sponsoring the type of videos I normally watch. But I don't see that type of ad on they type of videos I normally watch.
In fact - if I go to that exact video - and I do know which video it is and I also know the type of content uploaded by that particular user - and I also know what type of of content is displayed on the websites that that particular user links to. But when I watch that video - the ad for me is for some custom wheels for street car - and that's because I like motorsports and I watch many motorbike and car race video.
And the fact is - If I stop the download stream on that that particular video - it reverts it back to the chosen thumbnail of that video - and the chosen thumbnail for that video is one carefully calculated to advertise sex. So you got exactly what you asked for .... due to your "habits".
And I will tell you the ugly truth - there is a lot more worse than dating ads to be found on the website if one chooses to go looking for them.