Jonnycakes is an interesting guy. He takes the most bubblegum pop tracks you can imagine and then he rewrites the lyrics, makes them about Borderlands 2 for some mental reason and then re-records the entire song acapella, using only a smattering of Borderlands gunshots for rhythm. If he wasn't so crazy I might call him a genius.
Last time he reworked Ke$ha's 'Die Young'. This time Jonnycakes has reworked a Justin Bieber song I totally haven't heard before [looks around nervously]. It doesn't have quite the same punch as his Die Young effort, mainly because that Ke$ha track, regardless of your thoughts on Ke$ha herself, was super catchy and instantly recognisable.
Still, great work from Jonnycakes. This is the kind of thing YouTube was invented for.
UPDATE: Urgh. Apologies. I made a big error here. Yep, it's obviously Counter Strike: Source. This was from the same person who made Borderlands 2 Ke$ha video so I just assumed it was another Borderlands 2 vid. I was listening to the video rather than actually watching it. Very silly of me. I'm going to leave the post as is so everyone can laugh at my stupidity. Again, sorry. Terrible job by me.