Regular Show - The Benson Theory

Have you ever wondered why is Benson, one of the main characters of Regular Show, is always angry at Mordecai and Rigby and threatens them that he will fire them? I have a theory.
We are going about 2 years prior to the series. Mordecai and Rigby just got their new jobs as groundskeepers at the Park with Benson as their boss. Of course, they both were slackers as they are currently in the series, but it was something else that makes Benson very angry.

Benson does not allow sex in the Park house.


So, a week passed after Mordecai and Rigby got their jobs.
"Hey dude, I'm going on date with a girlfriend.", said Rigby.
"So you have a girlfriend too, huh? Since when?" asked Mordecai. (This is NOT Eileen)
"Why do you give a damn?", Rigby answered.
"Whatever, dude, just get out of here.", said Mordecai.
"OK, OK! Jeez!", answered Rigby.
Mordecai knew what he was going to do.

He was going to have sex with Margaret.


So he called her and told her to come over. And she did, 20 minutes later.
There was a small talk between them, and they soon were starting to have sex. Benson just got in the house to give Mordecai and Rigby their first paychecks for a well done job as Mordecai was about to climax. Benson heard moaning coming from the two's room, and went to investigate.
He knocked at the door,
"Mordecai! Hey Mordecai! I've got some paychecks for you and your little friend here!" he said.
Mordecai couldn't hear it from the sound of him moaning.
"MORDECAI OPEN THIS DOOR RIGHT NOW OR I'M GONNA BREAK THEM DOWN!" Benson screamed.
Still nothing.
Benson quickly broke the door down and he saw them two having sex on Mordecai's bed.
He was obviously mad.
"Grrrrrr... MORDECAI! WHAT AM I SEEING?!"
"Oh no! Benson, sorry about this, I... I..."
"WHAT DID I TELL YOU ABOUT SEX IN THIS HOUSE?!"
Margaret realized that Benson forbid sex in the house, slapped Mordecai, and left the house.
"I was just about to give you these paychecks, but... They're both going to Rigby now because you didn't respect the rules. And by the way, where's Rigby?"
"He went to a date." Mordecai responded.
"OK then." Benson said as he was leaving the room, "And, another thing. If I ever catch you have sex here again, YOU'RE FIRED!"
He was respecting Rigby now more than Mordecai, but Rigby also did something that made Benson angry at him a bit later.
...
He ate his sandwich.
I'm not kidding. Benson was so hungry that he was about to eat himself. He made himself a sandwich and went to get something. Rigby was walking at that moment and noticed the sandwich on the table. As he was also hungry he ate Benson's sandwich.
Benson came back and noticed the last bit of his sandwich eaten by Rigby. He was so mad that he wanted him to make him another sandwich. And then said "IF YOU EVER EAT MY SANDWICH AGAIN, YOU'RE FIRED!".
And there you have it. Now you know the mystery. You should be proud of yourself.