While its original meanings has been distorted from its ancient Chinese origins, it is popular in Southeast Asia is a semi-curse word. Its rise to popular culture has been spearheaded by Southeast Asian movie "The Maid", where the main character's primary name is called "Ah Soon", who plays a retarded teenager.
Bob: Don't be a Soon.
Tom: Lets hang out at the mall.
Bob: Why are you being such a Soon?
Tom: I wish I could fly.
Bob: Don't Soon.
Bob: That moron Tom told me he could fly. What a Soon.
Tim: Wow, that's really quite Soon.
I will meet you soon.
I will tweet you soon.
Fan: It's been two weeks and they said SOON again
Quiseng: Hey guys we'll post dates SOON
Fan: It's been six weeks where are my dates
Martinez: We won't post anytime SOON
Fan: GUYS they finally posted the dates
Your response of "on" means that something is giving you 100% satisfaction as opposed to the polar opposite 0%, which is off, just like an on and off switch. There's no in between.
Your friend tells you he's enjoying pizza. You are enjoying the pizza as well. You are both enjoying the moment. Your friend says "This pizza is so good" and then you nod your head and respond It's "So On."