You're nothing but Garbage: The Glee Club's treatment of EJ throughout the episode "Cutesie Badger" Some of the things they do to him include:

Not letting him join the Glee Club,

Thinking he'd be a horrible Brother,

Getting annoyed with EJ telling jokes but thinking Cutesie saying them is cute,

When EJ says something rude about Cutesie (which he didn't mean), his friends get so mad at him that they all tell him to leave the Headquarters and never come back, making him cry.

At first Sonic is shocked by these actions, but his shock quickly turns to outrage, and when the Club tells him to leave and never come back, he ever so angrily screams "WHAT THE HECK IS WRONG WITH YOU?!!!" and screams that despite what his half-brother did, he wouldn't be mad at him, and says that the Glee Club (Molly, Deema, Gumball, Darwin, Patrick, Spongebob, Nicole, Richard and Helen Lei) are the worst friends in the history of programs and leaves them in a huff, swearing he will never talk to them again.

Here is the first offense:

EJ: Hey! Can I join?

Molly: After all the point-outs, you think we'll let you join?

Here is the Second Offense:

Gumball: You know, Sonic? I don't think he's a very good role model for a brother.

Here is the third offense:

Cutesie: You're not singing in the perfect sense!

The Glee Club (except Sonic): Awwwwwww!

Here is the last offense:

EJ: (surprised) WHAAAAAAT? You would let him join?

Cutesie: Why? Why does my brother hate me?

EJ: (feeling sympathetic) Aw, dude, I didn't mean it.

Gumball: EJ, that was so....awful!

Helen Lei: Outrageous!

Darwin: Disgusting!

Molly: I think you need to go!

EJ: (confused) Where? Go where?

The Glee Club (except Sonic): AWAY!!!

Deema: And don't you dare come back!

EJ: (outraged, then downtrodden) Ok! So this is the way it's going to be. I hope you're happy. (Crying)

Sonic: (enraged) WHAT THE HECK IS WRONG WITH YOU?!!!!! Despite what he did to Cutesie, I wouldn't have gotten mad at him. And I'll come right to the point.

Patrick: What point?

Sonic: (still enraged) That you guys are the worst, most horrible friends I have ever seen in the history of programs!

Deema: Come on, Sonic! We can't play without you!

Sonic: (still enraged) NO! I'm done hanging out with you! You are not my friends! AND I'M NEVER TALKING TO YOU AGAIN!!!!!!!