Work is only as fun as the employees make it

Being a college student, I am allowed to have just crap jobs that I make little and do little.
I work at Pac Sun which is a unbelievably easy job and basically my manager made one big mistake.

She clearly told me I cannot quit, or be fired due to the fact that if that happened other people would end up quitting also.
I know, I know, "what a popular guy" ... Ha, no I just know how to have fun at work.

One day, it was fairly slow and it ended up being four people working in the store. We have two phones, one in the back room and one at the registers. My manager who for some reason enjoys leaving me in charge while she gets stuff done in the back has no idea what I am thinking.
I look over at the two girls I work with and ask them "You ever prank called your boss?" ... They both get this very concerned face and say "no, that would be stupid! People get in trouble doing that!" I couldn't help but laugh.. Remember the store is dead, I wouldn't do this if it was busy obviously..unless I was quitting.

Which is a brilliant idea, quit over the phone, while working! okay sorry back to my story.

I pull out my cell phone and go down to the saved contact "Pac Sun", yes it is saved I gotta call or avoid calls from time to time. It starts ringing, the two other girls were off doing something else and completely stopped and their jaws dropped. My manager in the back answers "Pac Sun, how can I help you?"
Me- "EH! My son bought a damn skateboard at your store and I need to return it!"
Her- "Um, sir, we don't sell skateboards."
Me-"I am holding the DAMN reciept and it says Pac Sun clearly on it!"
Her- "No, we don't sell skateboards here, just clothes."
Me-"Well I want my damn money back and I need to know where you guys are located!"
Her- "The address is on the reciept, I am sure you will be able to find us that way. Thank you" .... click..

The phone call was actually longer, I just condensed it down for attention deficites people tend to have.

All of this was going on and the girls I was working with are just cracking up finally...
My manager comes out and notices them laughing and says "Wow, I just got the most random weird phone call ever!"... The girls instantly start laughing and she says "Why are you guys laughing." and looks right at me... All I could say was I have no idea I think they are on drugs.
She looks at me and says she heard laughing in the background and that she knows I was screwing with her now.
All I say is "Go look at the door in the backroom, on the poster it clearly says "Work is only as fun as the employees make it!"
She just looks at me and walks away... Not a single word.