It's pretty normal dog behavior. Not all dogs do it, but it doesn't matter whether they are fixed or not. Some dogs are oblivious to it and some (Esther, for example) will not tolerate it and will rip the humper a new one.
For that reason, dog owners will sometimes discourage their dogs from humping.
But funny? Nope.
BTW, people who register specifically to post a YouTube video are usually banned as spammers, but I thought you might enjoy some feedback.