First and foremost when you're doing comedy, you gotta be relevant and applicable to the times that you're living in. When you try and just do comedy about who is dating who and lifestyle jokes, it gets tiring after a while. It's hard to be funny in that realm.
As far as what makes a viral video, then it's gotta be something that you've either never seen before, a fresh piece of comedy, or something that relates to something topical.