"Chillin' Like Penicillin" means taking advantage of global price parities to make your unemployment checks turn into a neverending tropical vacation in a third world country, but then becoming so entangled in local politics that you have to imititate a spider in every aspect, simply to stay alive.
The "Purple Fishes" is that weird feeling of dread one experiences when reading other people's journals backwards, letter-by-letter, aloud.
"Lake Stupid" is another name for the kitchen, so named because if you try to swim or catch fish or even skip stones there, you're a bleeding wanker.
"Tastes Like Herring!" is an exclamation of world-shattering desolation, to be spoken when an attempt to sing along with a song you don't know as well as you think resulting in singing half a word out loud when the actual song has broken into instrumental. It is a term of hopelessness; when you shout, "Tastes Like Herring", it means that you're probably going to pull out of society completely in shame, possibly by "Chillin' Like Penicillin"
"The Tapeworms Know All!" is just a friendly greeting. It's traditionally spoken by people who know what the secret bonus slang term "Pants! Pants! Pants!" means, but don't want to ever use that term around outsiders, for fear that the meaning will become clear by context.