I think we can somewhat offer Google the benefit of the doubt here too. It's likely that there's someone else targeting Google's algorithm to get that spammy video suggested to as many people as possible.

As you (mcphilip) said you don't have a YouTube account, so presumably Google has less data on what you might like or dislike. Suggesting more relevant results to you means that Google needs more data about what you like individually. It's balancing that whole "tracking me is evil" vs "showing me stuff I actually want to see is good".

I stay logged into my G+/YouTube account and the suggestions I get are generally acceptable, sometimes even great. I've never found them outright obnoxious in my case.