Simon's dismissal of Carli wasn't nearly brutal enough.

Had to keep it like that so that when he said you won't see me again, Carli could have the punchline of sorts by pointing out the times in the future where their paths will have to cross such as his mom's and his brother's birthday.

Could they have taken the route of Simon going off on Carli? Probably. However, this way they had a comic scenario set up that was easy to use and subverted the classic breakup line where one person says "you'll never see me again" or something to that effect.

Totally 100% agree! Should have been a lot sooner as well. One of the few sensible things Jay has ever said was calling her a *beep*

Bear in mind, Simon wasn't a great catch himself in a lot of ways.

In one of the episodes he invited himself round Carli's house drunk, painted on her driveway and then vomited on her little brother. Simon was lucky she talked to him after that. In a different episode, he got drunk again and climbed through her front window, believing it to be her bedroom only to find her little brother. Yes, we the audience understood the misunderstanding, but if that happened in real life, he'd be lucky to escape being arrested. Even if people believed that he was looking for Carli, getting drunk and climbing through her window in the middle of the night is a creepy thing to do.

Not defending Carli's actions in this movie, because she was in the wrong. Merely pointing out that there was wrong on both sides.

In terms of answering the original question though, in this movie I believe the point was that Simon realised she wasn't worth chasing any more. After doing so, there wasn't really any revenge that was needed. He realised there were plenty more fish in the sea, he was chasing somebody who wasn't interested, and that was it. He didn't want or need revenge, because he was over her. If he'd have tried to get revenge, it'd have proved he still cared what she thought in some way. He didn't, and that was that. He was off her hook.