So unfunny, it hurts.
This isn't supposed to be funny, its actually about the life of Timmy and how it deteriorates. What you don't understand is that there is deep thought put into making these videos. The reason Timmy gets into drugs is because his parents have been harassing him for years just because of what he enjoys doing. Thus, causing Timmy to get into drugs, the drugs make him lose control and end up killing his friends and loved ones. Its a tragic story. The reason Cosmo is into drugs is because he's sick of taking care of Poof. Poof isn't in this episode because he was at daycare, the main reason Timmy wanted to become older was because he was sick of dealing with his parents and he wanted to become older so he'd be able to do what he wanted to in his own eyes, but it turned for the worse as he noticed how scary it could be to be 21.
tl;dr its a story about a boy who grows up too early, faces life too fast and finds a terrible solution.