What perfume were YOU wearing? :-)
Actually, many YT'ers have different opinions. Some feel it's natural and allow it (usually with stuffed animals), some feel it's dominant behavior and needs to be curbed. For me, I find myself somewhere in the middle. Coby doesn't hump much at all, but his older brother Reggie does every once in a while (usually trying to use Coby as his stuffed animal).

I typically try to discourage it if it gets out of hand, not so much that I think it's harmful or dominant, but just because if I have company, I don't want them showing off!!