There are a lot of 'wtf man, this video sucks if you want a good home made nude videos click xxxxx' comments in the youtube comment sector. even if the video is nothing to do with nudity, they may still got the same spams. for IOS games related videos in youtube, there are a lot of spams about how to get the game free.
Even benign YouTube vids (I think I once saw one on a freddiew video) will occasionally have those kinds of comments. It's just spam.
If people didnt click on stupid spam links, or people didnt buy products online from spammers we 'might' get less and less spam on websites/forums/all over the place. The second you click on these links it helps the spammers. I mean some idiots have to buy viagra and other stuff from spam emails or they wouldnt bother.