At the start of Weo Weo Weo, we see a man hearing headphones shooting himself in the head. This was actually a warning to headphone users as the video was very loud.
Urf Rap is full of well-hidden puns. For example, near the end of the song after talking about horses for the entire song he asks "Is this song complete? / Nay (Neigh)"
His final score for Half-Life 2 is a 3 out of 5. The description of the video talks about Half-Life3.