These are hilarious, but I'm not familiar with the term "viral video". What does it mean?
A viral video is a small clip (like on youtube, snotr, etc) that is so hilarious/awesome/shocking that becomes instantly popular shared with everybody and their grandma. So take the "look I'll say I'm sorry" clip. That actually happened, it went on the news, it was not an intentional thing, and people immediately thought it was so awesome/hilarious that they posted a clip on YouTube, told their friends to watch it, they told their friend , people saw the views on the clip and they watched, and to infinity. But that was an unintentional viral video. There are a lot of intentional viral videos as well, like the (I suspect) "1991 beard off competition." There are companies whose sole purpose is to make viral videos and marketing campaigns, as well as make funny videos. Why? I'm sure they make money in some way and so on as well as gaining a reputation as a funny marketing firm or production company.
Here are some more that I have just found (or knew about but want to post) that are utterly hilarious.
! This is a clip from a World of warcraft game. Basically a whole team is planning out some super strategy to get a piece of equipment for a team mate, a guy by the name of Leroy Jenkins. Apparently, Jenkins got a little too impatient. I am amazed at how popular this video actually is, since the guy has used the video to become an internet sensation, game presenter, and spawn multiple knockoffs on movies such as Year One."
(fast forward to 1:15 to get to the funny bit)
YouTube - Leeroy Jenkins
Its energy in the can apparently. But be careful, nature will tell you slow down, and you will be like, F you and kick her in the face with your energy legs.
YouTube - Powerthirst
I defy you to watch this no less than 3 times.
YouTube - Dramatic Look
"Christian the Lion"
This one is just neat. These two brothers saved a little lion cub from an abusive owner and nursed it back to health. The brothers then had to send the lion to a nature preserve because they could not take care of it anymore. 20 years later they found the cub they had nursed back to health. The reunion is pretty awesome. Note:, It may be best to mute the corny song.
YouTube - Christian the Lion - the full story (in HQ) [minus 20 million views!!]