Soggy Sandwich Day is on May 17th and is celebrated by spilling any beverage, on anybody's sandwich, whether it be your own or a friend's (it is required that you say "Soggy Sandwich Day!" before spilling the beverage on a friend's sandwich).
You: Hey dude, guess what?
Dude: What?
You: ... It's Soggy Sandwich Day (proceeds to spill beverage on sandwich)
Dude: AHHHHH
It is THE BEST channel on the youtube in the history of mankind. And also womankind because they are all inclusive. It also means that you are fricking amazeballs, and you have big penis.